Fix URLs to the GraphQL Specification and its repository

Replicates graphql/graphql-js@8d0314d

Author: Cito

README.md

@@ -34,8 +34,8 @@ examples.
 ## Getting started
 
 An overview of GraphQL in general is available in the
-[README](https://github.com/facebook/graphql/blob/master/README.md) for the
-[Specification for GraphQL](https://github.com/facebook/graphql). That overview
+[README](https://github.com/graphql/graphql-spec/blob/master/README.md) for the
+[Specification for GraphQL](https://github.com/graphql/graphql-spec). That overview
 describes a simple set of GraphQL examples that exist as [tests](tests) in this
 repository. A good way to get started with this repository is to walk through that
 README and the corresponding tests in parallel.