UnderScore In request header is replace with -

I have noticed that _ in request header are being replaced with -  .

```
Create Http Context     192.186.1.123       http
Set Request Header  client_id           myclient
Set Request Header  response_type       positve
POST                /api/oauth2/authorize   

```

When I see the request via https shark, I see client_id is sent as Client-id. Due to this my request is failing. 
