run chruby_auto before every command
run chruby_auto before every command

With recent changes, chruby_auto wrapper is smart and fast enough to run on
every command with minimal impact.

Only slowdown left is when actually switching rubies, which shouldn't happen
too often.

JeanMertz/chruby-fish,rstacruz/chruby-fish,JeanMertz/chruby-fish,rstacruz/chruby-fish