ci: fix invalid dates for go 1.13 modules

Created by: ggilmore

Go 1.13 now performs additional verification on version strings in go.mod files. It seems like some of our dependencies (and transitive dependencies) have malformed timestamps. I am not sure how this occurred.

According to https://golang.org/doc/go1.13#version-validation, the solution is to replace those malformed version strings with just a commit hash. This PR is the result of me doing so along with running go mod tidy afterwards.

See:

• https://github.com/golangci/golangci-lint/issues/659#issuecomment-527854777
• https://groups.google.com/forum/#!topic/golang-nuts/9AYsrmYt37s