Updates ruby version in readme
Moves from .rvmrc to .ruby-version

Note from RVM:
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 warning with 'rvm
rvmrc warning ignore /Users/duksis/code/extreme_startup/.rvmrc',
'.rvmrc' will continue to be the default project file in RVM 1 and
RVM 2, to ignore the warning for all files run 'rvm rvmrc warning ignore
all.rvmrcs'.