Fix git address in example pre-commit yaml

The git@ syntax requires an SSH key with permissions to the repo.

I was getting this error using the example:
```
$ pre-commit autoupdate
Updating git://github.com/pre-commit/pre-commit-hooks...already up to date.
Updating git@github.com:FalconSocial/pre-commit-python-sorter.git...An unexpected error has occurred: CalledProcessError: Command: (u'git', u'clone', u'--no-checkout', 'git@github.com:FalconSocial/pre-commit-python-sorter.git', u'/home/sdet/.pre-commit/repom4RjDu')
Return code: 128
Expected return code: 0
Output: (u"Cloning into '/home/sdet/.pre-commit/repom4RjDu'...\n", u'Permission denied (publickey).\r\nfatal: The remote end hung up unexpectedly\n')
```
After this change:
```
$ pre-commit autoupdate
Updating git://github.com/pre-commit/pre-commit-hooks...already up to date.
Updating git://github.com/FalconSocial/pre-commit-python-sorter...updating 1.0.1 -> 31865d04ebd9961fb5fd4fb57ec4016c1db0bbe4.
```