write bundler version
Fix bundler git gemspec bug.

Bundler 1.3.0.pre.8 broke backwards compatibility with gemspecs.
6548e31e8ad061403d65505d7d2e17c489b262cc changes how gemspecs are being
generated which is causing problems with git gemspecs that are not self
contained. See https://gist.github.com/hone/5043f02bea633fd1a844 for the
differences in the gemspec.