Broken `platfrom`

Just compare how it works in the initial commit (my first version) and now - it returns incorrect results

```
ua -e -n chrome -o linux

{
   ...
  "platform": "X11; Linux x86_64", 
   ....
}
```
When it should be `Linux x86_64`. The same thing with other OS.
For now the `platform` key of JS navigator returned by this lib is wrong.
