rules_go v0.20.0, v0.19.6 and gazelle v0.19.0 are now available

[Jay Conrod]

rules_go v0.20.0 has updated dependencies and more bug fixes. It removes support for Go 1.10, 'objc = True' and related attributes.

rules_go v0.19.6 has bug fixes for cgo, linking, and bazel_testing.

gazelle v0.19.0 has improved repository rule management, improved visibility between submodules retrieved with go_repository, and several more minor features and bug fixes.