v1.6.0

v1.6.0
Version 1.6.0

Release to drop support for Python 2.6 and add support for google-auth.

• Support for Python 2.6 has been dropped. (#319)
• The credentials argument to discovery.build and discovery.build_from_document
  can be either oauth2client credentials or google-auth credentials. (#319)
• discovery.build and discovery.build_from_document now unambiguously use the
  http argument to make all requests, including the request for the discovery
  document. (#319)
• The http and credentials arguments to discovery.build and
  discovery.build_from_document are now mutually exclusive, eliminating a
  buggy edge case. (#319)
• If neither http or credentials is specified to discovery.build and
  discovery.build_from_document, then Application Default Credentials will
  be used. The library prefers google-auth for this if it is available, but
  can also use oauth2client's implementation. (#319)
• Fixed resumable upload failure when receiving a 308 response. (#312)
• Clarified the support versions of Python 3. (#316)