heroku/heroku-buildpack-nodejs — pull request #84 by mojodna (2013-12-13 21:49:58+00:00)
Title: Set $NPM_REBUILD to rebuild cached deps

When composed with other buildpacks, underlying dependencies (e.g. [mapnik](https://github.com/mojodna/heroku-buildpack-mapnik) may have changed causing the cached binaries to link to incorrect versions. If prior buildpacks (or users) set `$NPM_REBUILD`, cached modules will be rebuilt.