Bad error message on incorrect path provided

I used a path `foo/bar` instead of `/foo/bar` and CLI returned an error with message: `#/paths must NOT have additional properties`. That seems very confusing.

 On [Swagger editor](https://editor.swagger.io), the provided error message is 
<pre>Structural error at paths
should only have path names that start with\`/`
</pre>,which seems way better.