Convert .rvmrc to .ruby-version

You are using '.rvmrc', it requires trusting, it is slower and it is not compatible with other ruby managers,
you can switch to '.ruby-version' using 'rvm rvmrc to [.]ruby-version'
or ignore this warnings with 'rvm rvmrc warning ignore /Users/bklang/src/adhearsion-website/.rvmrc',
'.rvmrc' will continue to be the default project file in RVM 1 and RVM 2,