1681 [google_sign_in] Add missing template type parameter to invokeMethod calls. Bump minimum Flutter version to 1.5.0. Replace invokeMethod with invokeMapMethod wherever necessary. (cla: yes)

1682 [firebase_auth] Document support email requirement in README (cla: yes)

1683 [image_picker]Add missing template type parameter to invokeMethod calls. Bump minimum Flutter version to 1.5.0. Replace invokeMethod with invokeMapMethod wherever necessary. (cla: yes)

1684 [in_app_purchase]Add missing template type parameter to invokeMethod calls. Bump minimum Flutter version to 1.5.0. Replace invokeMethod with invokeMapMethod wherever necessary. (cla: yes)

1685 [connectivity] android: Respect case TYPE_MOBILE_HIPRI (cla: yes)

1688 [google_map_flutter] correct version (cla: yes)