Bring License in line with graphql-spec

[orta]

/cc @leebyron / @jchris who should probably decide

Based on this comment by @IvanGoncharov graphql/graphql-js#1960 (comment)

It looks like this repo should go MIT for consistency, if so we can merge #703 now - if no responses I'll give it a merge in 3 months (chance for anyone to give feedback), as I think it's the right thing to do 👍

[carolstran]

Left a review on #703 and referenced this issue - it'd be great to get that merged if possible 🚀

[IvanGoncharov]

@carolstran @orta I started the relicensing process with GraphQL Foundation.
Can take some time since we need conformation from FB as previous copyright owners, will keep you updated.

[Urigo]

We can close this as this repo is now MIT