Version command only works with directory

Created by: mxstbr

I tried to get the version of create-react-app I had installed globally and thus ran

$ create-react-app --version

Which gave me this output:

Usage: create-react-app <project-directory> [--verbose]

By specifying a directory the version output works perfectly fine, but doesn't actually create a directory:

$ create-react-app test --version

create-react-app version: 0.1.0

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I realize that this would be a change in the global CLI, but I think the new behaviour is much nicer and less confusing, and people who don't have the newer version installed won't have any problems either.

PR for this: #152