Minor update of graphql-relay-py, based on graphql-relay-js 0.8.0, and compatible with graphql-core version 3.1.7.
Changes:
* `unbase64` now returns an empty string on errors (39)
* Use standard base64 implementation (5032f9355d53d830a02ab7bb4e27b7735ca3ef76)
* `array_connection` returns all elements if cursors are on the outside (3ba3aa2bd6dc6306021f1cac17f7913c5f6d56e5)
* Allow mutations to return mappings (c5d0407323145c23acdd0480f72fe91de9100808)