Migration way of old plugconf file is needed

[tyru]

After deprecation commit of s:config() (c9851a2),
volt build shows a lot of warnings for old plugconf files.

$ bin/volt build 
[INFO] Full building /home/tyru/.vim/pack/volt/opt directory ...
[INFO] Installing vimrc and gvimrc ...
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/vim-volt/vim-volt.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/capture.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/Shougo/neosnippet.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/Shougo/neosnippet-snippets.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/nextfile.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/closesubwin.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/markdown-codehl-onthefly.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tpope/vim-markdown.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/kana/vim-textobj-user.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/vim-jp/vimdoc-ja-working.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/quickey.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/stoptypofile.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/thinca/vim-quickrun.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/vim-jp/autofmt.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/thinca/vim-prettyprint.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/thinca/vim-themis.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/karakuri.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/fatih/vim-go.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/Shougo/context_filetype.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/posva/vim-vue.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/vim-jp/vim-vimlparser.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/open-browser.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/open-browser-github.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/caw.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/vim-jp/vital.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/homevim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/hotwatermorning/auto-git-diff.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/cespare/vim-toml.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/kannokanno/vmock.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/mmisono/viminesweeper.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/vital-sunaba.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/syngan/vim-vimlint.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/kana/vim-repeat.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/nesk.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/w0rp/ale.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/tyru/transbuffer.vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/Quramy/tsuquyomi.vim:
* s:config() is deprecated. please use s:on_load_pre() instead
[WARN] parse warnings in /home/tyru/volt/plugconf/github.com/leafgarland/typescript-vim.vim:
* s:config() is deprecated. please use s:on_load_pre() instead

It is painful to rewrite all of these files.
Volt should provide a migration way of this.