v2.6.0

Features

• add always_use_jwt_access (#334) (ae67d10)

Bug Fixes

• deps: pin 'google-{api,cloud}-core', 'google-auth' to allow 2.x versions (#356) (a970dd2)
• disable always_use_jwt_access (#342) (a95e401)
• enable self signed jwt for grpc (#360) (707fad1)

Documentation

• omit mention of Python 2.7 in 'CONTRIBUTING.rst' (#1127) (#327) (faa6fb9), closes #1126
• add Samples section to CONTRIBUTING.rst (#357) (8771716)