IDs must not contain spaces

[ad-si]

According to the GraphQL spec IDs must not contain spaces. So I think the toJson function should actually be toJson : Request a b -> Result Error Value so that GraphQl.field "field with space" would cause an error.

[ghivert]

I'm no more working on Elm in my daily life, I can try to add it to the library, but this will take some time.

On the change, I agree it would be better. I'll see to implement it.