Push tags and publish at end of postversion script
Push tags and publish at end of postversion script

This will help avoid situations where maintainers publish a new release
to npm registry, but forget to push the new tags to GitHub.

Like this one:

https://github.com/sinonjs/sinon/issues/2393

cjohansen/Sinon.JS,cjohansen/Sinon.JS,cjohansen/Sinon.JS