u- return alias field

[wenj91]

query:

{
    hello{
        idAlias:id
        id
        world
    }
}

return:

map[string]interface{} {
    "idAlias": 1,
    "id": 2,
    "world": "world"
}

before result:

{
    "idAlias": 2,
    "id": 2,
    "world": "world"
}

expect:

{
    "idAlias": 1,
    "id": 2,
    "world": "world"
}

this PR fix this issue

[coveralls]

Coverage decreased (-0.02%) to 91.971% when pulling 424d61d on wenj91:master into f02a1c9 on graphql-go:master.

[astudnev]

I met with the same issue... any plans to merge it?