Aliases are not supported in map keys

when i query

```
{
hello{
alias1: id
alias2: id
}
}
```

and submit the map
```
{
hello{
alias1: "1"
alias2: "2"
}
}
```

it returns nil for both aliases

Expected result is alias1 :"1" and "alias2": "2"

There is another case... when i query
```
{
hello{
id
alias2: id
}
}
```

and submit the map
```
{
hello{
id: "1"
alias2: "2"
}
}
```

it returns alias2: "1" and id: "1"

Expected result is id :"1" and "alias2": "2"

both results are wrong!

It may be covered in PR https://github.com/graphql-go/graphql/pull/630 but i have not tested all possible cases