Gracefully handle configuration error in JSCS hook

The error message output by `jscs` when no configuration file is present
changed at some point since this hook was first written.

Change the check to inspect the exit code of the process. Looking at the
source at https://github.com/mdevils/node-jscs/blob/master/lib/cli.js,
the CLI appears to return 2 when a lint was found, 1 when some other
problem occurs, and 0 when no lints were found.

Change-Id: Id1a1d7b6d751f17edc03cea3960701ba728246f7
Reviewed-on: http://gerrit.causes.com/40418
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>