Embed nginx-1.5.0.tar.gz (1.1MB) in buildpack

Rather than downloading nginx-1.5.0.tar.gz from Dropbox; this embeds it in `vendor/nginx-1.5.0.tar.gz`

This has 2 benefits
* Removes a dependancy on dropbox (which can be slow from non US CF installations)
* Enables "offline" usage of the nginx buildpack when it has been uploaded via `cf create-buildpack`