Adjust the GitHub GQL schema to use spec-compliant descriptions

It looks like the string literal style for descriptions in the schema language is becoming the standard.

Sources:

- graphql/graphql-spec#466
- https://stackoverflow.com/questions/39962867/how-do-i-add-a-description-to-a-field-in-graphql-schema-language
- https://medium.com/apollo-stack/all-you-need-to-know-about-graphql-js-0-7-921e75dd7fd1#.t9csdknur

Author: tomhoule

graphql_query_derive/src/tests/github.rs

@@ -14,13 +14,17 @@ fn ast_from_graphql_and_json_produce_the_same_schema() {
     let graphql_parser_schema = graphql_parser::parse_schema(SCHEMA_GRAPHQL).unwrap();
     let json = Schema::from(json);
     let gql = Schema::from(graphql_parser_schema);
+
     assert_eq!(json.scalars, gql.scalars);
     for (json, gql) in json.objects.iter().zip(gql.objects.iter()) {
         assert_eq!(json, gql)
     }
     for (json, gql) in json.unions.iter().zip(gql.unions.iter()) {
         assert_eq!(json, gql)
     }
+    for (json, gql) in json.interfaces.iter().zip(gql.interfaces.iter()) {
+        assert_eq!(json, gql)
+    }
     assert_eq!(json.interfaces, gql.interfaces);
     assert_eq!(json.query_type, gql.query_type);
     assert_eq!(json.mutation_type, gql.mutation_type);