Drop `platform` dependency

Pros:
* Less dependencies, smaller package

Cons:
* HTTP header User-Agent won't contain info about calling platform 


```
without platform:
    route4me.js  56.8 kB       0  [emitted]  main
with platform:
    route4me.js  70.1 kB       0  [emitted]  main
```

could affect on  #16 (without `platform` package will be  easier) 