cmd/go/internal/get: warn about -insecure deprecation
Adds deprecation warning for -insecure flag on go get in both modules
and GOPATH mode.
Updates #37519.
Change-Id: Ie2efeeb4a91e6dda92955295969e9715314ae50e
GitHub-Last-Rev:
a9ebe21fe067baa12391ad4f9357d8e5b0cf7051
GitHub-Pull-Request: golang/go#41497
Reviewed-on: https://go-review.googlesource.com/c/go/+/255882
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>
Trust: Michael Matloob <matloob@golang.org>
Trust: Jay Conrod <jayconrod@google.com>