Merge pull request #198 from heroku/reremove_vulcan_tasks

Reremove vulcan tasks
Merge pull request #199 from heroku/schneems/bundler-1.5.2

Bump to bundler 1.5.2 which includes parallel fix
bump to v91
changelog
fix stash checking for buildpack:increment
add messaging around buildpack increment success
Merge pull request #204 from heroku/fix_buildpack_increment

Fix buildpack increment
raise an error if problems detecting the bundler vendor directory
figure out slug vendor base without munging in errors
add tests for user env compile
Merge pull request #203 from heroku/stderr

Fixes #202
Use ruby-git gem via https instead of git protocol

Most corporate firewalls block the git:// protocol. Use https:// instead
to allow the ruby-buildpack to be built in corporate firewalls.