Merge pull request googleapis#907 from dhermes/cut-release-0.5.1

Upgrading version to 0.6.0.

Merge pull request googleapis#813 from dhermes/cut-release-0.5.0

Upgrading version to 0.5.0.

Merge pull request googleapis#723 from dhermes/cut-release-0.4.3

Upgrading version to 0.4.3.

Merge pull request googleapis#678 from dhermes/cut-0.4.2

Upgrading version to 0.4.2.

Merge pull request googleapis#645 from dhermes/fix-new-docs-on-tag

Making sure new docs get built on tags.

Merge pull request googleapis#598 from dhermes/update-version

Updating to version 0.4.0 for PyPI release.

Merge pull request googleapis#391 from silvolu/pre-03

Remove keys and update minor