[issue-767] Remove backslash in puppet-lint log format (refs: #767)

Hi, this PR solve my problem with issue #767

Puppet-lint format before :
```bash
$ puppet-lint /tmp/foo.pp --log-format "\%{KIND} [\%{check}] \%{message} at \%{fullpath}:\%{linenumber}"
\ERROR [\autoloader_layout] \foo not in autoload module layout at \/tmp/foo.pp:\1
\WARNING [\documentation] \class not documented at \/tmp/foo.pp:\1
```
 Puppet-lint format after :
```bash
$ puppet-lint /tmp/foo.pp --log-format "%{KIND} [%{check}] %{message} at %{fullpath}:%{linenumber}"                                                                                
ERROR [autoloader_layout] foo not in autoload module layout at /tmp/foo.pp:1
WARNING [documentation] class not documented at /tmp/foo.pp:1
```

Thanks ```let g:syntastic_debug=1``` :-)