Fix for the cowboy_rest template

The default cowboy_rest template give an error when used as it is.

```
Error in process <0.156.0> with exit value: {function_clause,[{lists,sort,['_'],[{file,"lists.erl"},{line,478}]},{cowboy_rest,match_media_type_params,5,[{file,"src/cowboy_rest.erl"},{line,315}]},{cowboy_protocol,execute,4,[{file,"src/cowboy_protocol.erl"},{line,435}]}]}
```