Warnings from bundler and rvm

[bkleinen]

Hi, I wanted to use & modify link-checker for my own usage and started off getting warnings from rvm (about the .rvmrc script that it was about to execute) and from bundler ( about the deprecated :rubygems source).

I've updated all this and switched to ruby 2.0.0 on the way. Would be great if you consider merging this in, might help others getting started contributing to the project.