node multibuildpack spec

tests #261
Test default process types added with Procfile

When a Procfile is present, default process types should still be added.
Merge pull request #262 from heroku/schneems/node-multi

node multibuildpack spec
Merge pull request #263 from heroku/schneems/empty-procfile

Test default process types added with Procfile
update changelog
bump to v117
[close #247] bundle platform with user env args
setup GEM_PATH so rubygems can find bundler
remove bundler setup since it affects BundlerWrapper tests
don't overwrite travis's PATH

the PATH matters b/c the binstubs pick up the ruby based on the ruby in
the path: `#!/usr/bin/env ruby`.
git add . is weird on travis
preserve RUBYOPT except for BundlerWrapper tests
Merge pull request #254 from heroku/schneems/fix-platform-env-arg

[close #247] bundle platform with user env args
remove debug test output
fix ruby patchlevel support
Merge pull request #268 from heroku/schneems/patchlevel

Fix patchlevel support
bump to v118
changelog
[ci skip] fix date
temporarily disable default-cache