Don't ship _config.yml

[michaelpj]

If the config file is included in the gem, then it will be applied to
users' site configurations alongside their own configuration.

This doesn't provide much benefit, since most of the configuration
options are either a) not applicable to users (e.g. the title setting),
or b) easily set by users to their own preferences (e.g. the markdown
settings).

Furthermore, some of the settings are actively harmful. In particular the paginate
options are from the old jekyll-paginate. In recent versions of
Jekyll, setting the old options causes build failures for users who are
using the newer jekyll-paginate-v2.

Overall, I think it's useful to have _config.yml in the repository as
an example, but I don't think we should ship it.

[yous]

Thanks for pointing this out. I'll release a new version of the gem soon.

[michaelpj]

Thank you! No need to hurry on my behalf, I've worked around it locally for now :)