Download tar of compiled nginx binaries rather than use package

[stuart-warren]

Hi,

All other buildpacks I've seen follow 12factor principles and "vendor" any required dependencies into the app directory. Take an Apache buildpack for example https://github.com/Kloadut/heroku-buildpack-static-apache/blob/master/bin/compile

The package approach causes issues with other PaaS like Deis who use a separate runner container to the builder which only has the contents of the builddir. see: deis/deis#1796

[stuart-warren]

See https://github.com/neilmiddleton/heroku-buildpack-nginx/blob/master/support/package_nginx