Detect manifest-(fingerprint).json instead of manifest.yml for rails4

[brettgoulder]

manifest.yml is not created in rails4 anymore, it's manifest-(fingerprint).json

https://github.com/heroku/heroku-buildpack-ruby/blob/master/lib/language_pack/rails4.rb#L40

[schneems]

(╯°□°）╯︵ ┻━┻)

[hone]

oops! how is the fingerprint generated?

[brettgoulder]

I think here: https://github.com/sstephenson/sprockets/blob/master/lib/sprockets/manifest.rb#L53

[catsby]

So on https://github.com/heroku/heroku-buildpack-ruby/blob/master/lib/language_pack/rails4.rb#L40-L57, change:

if File.exists?("public/assets/manifest.yml")
...
else

to

unless Dir.glob('public/assets/manifest-*.json').empty?
...
else

If you're like me and don't care for unless [...] else l, then just swap the code blocks. That work?

[hone]

I think that looks right.

[catsby]

@brettgoulder suggested if Dir.glob('public/assets/manifest-*.json').any? as opposed to the unless..else.

[hone]

Fixed by #74 .