Add entry for 5.1.0 to CHANGELOG

Add entries:
- #282 
- #284 
- #285

Author: aaron-lane

CHANGELOG.md

@@ -8,16 +8,23 @@ Extending the adopted spec, each change should have a link to its corresponding
 
 ## [Unreleased]
 
-### Changed
-
-* Made `region` variable optional for zonal clusters [#247]
+## [v5.1.0] - 2019-10-24
 
 ### Added
 
 * Added ability to skip local-exec provisioners. [#258]
 * Added [private](https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/tree/master/modules/private-cluster-update-variant) and [beta private](https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/tree/master/modules/beta-private-cluster-update-variant) variants which allow node pools to be created before being destroyed. [#256]
 * Add a parameter `registry_project_id` to allow connecting to registries in other projects. [#273]
 
+### Changed
+
+* Made `region` variable optional for zonal clusters. [#247]
+* Made default metadata, labels, and tags optional. [#282]
+
+### Fixed
+
+* Authenticate gcloud in wait-for-cluster.sh using value of `GOOGLE_APPLICATION_CREDENTIALS`. [#284] [#285]
+
 ## [v5.0.0] - 2019-09-25
 v5.0.0 is a backwards-incompatible release. Please see the [upgrading guide](./docs/upgrading_to_v5.0.md).
 
@@ -191,7 +198,8 @@ In either case, upgrading to module version `v1.0.0` will trigger a recreation o
 
 * Initial release of module.
 
-[Unreleased]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v5.0.0...HEAD
+[Unreleased]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v5.1.0...HEAD
+[v5.1.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v5.0.0...v5.1.0
 [v5.0.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v4.1.0...v5.0.0
 [v4.1.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v4.0.0...v4.1.0
 [v4.0.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v3.0.0...v4.0.0
@@ -206,11 +214,14 @@ In either case, upgrading to module version `v1.0.0` will trigger a recreation o
 [v0.3.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v0.2.0...v0.3.0
 [v0.2.0]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/compare/v0.1.0...v0.2.0
 
-[#258]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/issues/258
+[#285]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/285
+[#284]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/284
+[#282]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/282
 [#273]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/273
-[#247]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/247
+[#258]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/issues/258
 [#256]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/256
 [#248]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/248
+[#247]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/247
 [#228]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/228
 [#238]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/238
 [#241]: https://github.com/terraform-google-modules/terraform-google-kubernetes-engine/pull/241