Quiet option incorrectly asks for an argument

```
$ ./gitcheck.py -h | grep -- -q
  -q, --quiet                          Display info only when repository needs action
$ ./gitcheck.py -q
option -q requires argument
```

In https://github.com/badele/gitcheck/blob/master/gitcheck/gitcheck.py#L472, `q:` should probably be replaced by just `q`.