Use the commit hash to refer to the Heroku geo buildpack
- See https://github.com/cyberdelia/heroku-geo-buildpack/issues/22 for a full explanation of why this is being done. tl;dr: There seems to be some weird caching issue that is preventing the right version of the GDAL et.al. from being installed when we just use the tag name for the geo buildpack.
Update Python buildpack version
Merge branch 'master' into heroku-deploy