Default PATH variable now excludes all entries within /app during builds

Change effective on 04 May 2017

At build time, the default PATH variable now excludes all entries within the /app folder. If a buildpack relies on a path previously set to a folder within /app, it needs to set it itself, either within the buildpack or the build folder.

For example, if a buildpack needs to install gems, it needs to explicitly set the GEM_PATH where they will be installed with the following:

export GEM_HOME=$1/vendor/gems
export GEM_PATH=$1/vendor/gems