How to access the arguments of a query within the RequestContext Object ?

### What happened?

Hi there,
When trying to obtain the variables from a request context Object (with `graphql.GetRequestContext(ctx).Variables` with the following query:
```
query MyQuery {
queryNode(filter:{isRoot:true}) {
name
}
}
```
I obtain a empty map.

### What did you expect?

` map[filter: map[isRoot:true]]`

Furthermore, I get the desired result if I use
```
query MyQuery($args: MyArgs!) {
queryNode(filter:$args) {
name
}
}

{ "args": {"isRoot": true}}
```

### versions
- glqgen : v0.11.3
- go: 1.14.1
- gqlparser: v2/v2.0.1