rm is useful if you need to pass arguments that would otherwise be
	hard to quote properly in the shell script. In the script, $0 will be
	"/bin/sh" and $1, $2, etc, are the positional arguments from Args.

5. Command with arguments:

	   "postCommit": {
	     "command": ["rake", "test"],
	     "args":    ["--verbose"]
	   }

	This form is equivalent to appending the arguments to the Command slice.

It is invalid to provide both Script and Command simultaneously. If none of the fields are specified, the hook is not executed.²