Remove `bundle exec` overdose and add link to Rubygems Bundler.
Remove `bundle exec` overdose and add link to Rubygems Bundler.

100star/guard,sideci-sample/sideci-sample-guard,yujinakayama/guard,baberthal/guard,ginkel/guard,pjump/guard,guard/guard,garettarrowood/guard,sdgdsffdsfff/guard