fix(Makefile): fix check-fleet Makefile target

Just a little indentation issue.

```console
$ make status
Your fleetctl client version should match the server. Local version: fleetctl version 0.5.0, server version: fleetctl version 0.6.2. Uninstall your local version and install the latest build from https://github.com/coreos/fleet/releases
make: *** [check-fleet] Error 1
```

For easy testing, check out #1541 without updating your local `fleetctl`.

fixes #1505