v0.7.1

• graphql-js parity v0.6.0.
• std's lib context @ https://github.com/graphql-go/graphql/pull/214
• no dependencies @ https://github.com/graphql-go/graphql/pull/218
• date time scalar @ https://github.com/graphql-go/graphql/pull/219
• enum type pointer values @ https://github.com/graphql-go/graphql/pull/220
• gqlerrors nil nodes check @ https://github.com/graphql-go/graphql/pull/221
• add types on runtime @https://github.com/graphql-go/graphql/pull/195