webpacker resolved_paths deprecated

[pgwillia]

Describe the bug
asset:precompile has failure after bumping webpacker.

NoMethodError: undefined method `+' for nil:NilClass
�[0m
�[91m/usr/local/bundle/gems/webpacker-5.2.1/lib/webpacker/configuration.rb:31:in `additional_paths'

https://stackoverflow.com/a/63530034 explains that resolved_paths has been deprecated and should be replaced by additional_paths

To Reproduce
Steps to reproduce the behavior:
https://hub.docker.com/repository/registry-1.docker.io/ualbertalib/jupiter/builds/10511763-b384-429a-81de-66296e5b0786

Expected behavior
The build is clean.

Screenshots
If applicable, add screenshots to help explain your problem.

[pgwillia]

SUCCESS! https://hub.docker.com/repository/registry-1.docker.io/ualbertalib/jupiter/builds/fd8c7d3f-53dd-4654-87c4-f927f4c4031f