clear cache on ruby_version change
cache_store can store files as well
chomp newline off of `ruby -v` output
load_bundle_cache -> load_bundler_cache
update copy
don't clear cache on new apps
update changelog
Revert "cache_store can store files as well"

This reverts commit 4bfc6dcab6ecf3c015b7b0eab402a7c3a7adef93.

This would lead to successive slug size increases, storing the vendor
directory into the vendor/bundle directory each time. Like:

vendor/bundle/bundle/bundle/....
use `vendor/heroku` for storing metadata b/t builds
cleanup mess from v37
always write ruby_version to the cache
can't cache_load a file
reinstall language pack gems since they live in `vendor/bundle`
update changelog
don't clear cache on new apps
actually purge the cache again on ruby version change
always need to reinstall language gems when clearing the bundler cache
update changelog
store the buildpack version in the cache
this actually should just be an elsif