Merge pull request google#555 from davidmorgan/release-6-2-0

Release 6.2.0.

Merge pull request google#530 from davidmorgan/analyzer-patch

Update for analyzer 0.33.3.

Merge pull request google#526 from davidmorgan/release-6-1-5

Release 6.1.5.

Merge pull request google#511 from efortuna/master

Modify pubspec to allow build package of 1.0 and greater

Merge pull request google#503 from davidmorgan/release-6-1-3

- Add `built_value_test` support for remaining built collections.

Merge pull request google#500 from davidmorgan/release-6-1-2

Release 6.1.2

Merge pull request google#496 from davidmorgan/release-6-1-1

Release 6.1.1.

Merge pull request google#486 from davidmorgan/release-6-1-0

Release 6.1.0.

Merge pull request google#467 from davidmorgan/release-6-0-0

Release 6.0.0.

Merge pull request google#463 from davidmorgan/bump-sdk

Allow SDK 2.0.0.