Load chruby auto-switching after setting default ruby

* If a new shell is opened in a directory containing a .ruby-version
  file, the auto script switches the ruby to the version specified, but
  the subsequent call to chruby manually changes it back to your default
  version. This leaves chruby in a weird state where RUBY_AUTO_VERSION
  is specified making the script _think_ it doens't need to change
  itself back.