cmd/go/internal/modfetch: stop cutting the last character of versions
cmd/go/internal/modfetch: stop cutting the last character of versions

When a zip archive for a module contains an unexpected file, the error
message removes the last character in the version number, e.g. an invalid
archive for "somemod@v1.2.3" would generate the following error:
"zip for somemod@1.2. has unexpected file..."

Change-Id: I366622df16a71fa7467a4bc62cb696e3e83a2942
GitHub-Last-Rev: f172283bcdffd45b485b1e8fd99795eb93fef726
GitHub-Pull-Request: golang/go#27279
Reviewed-on: https://go-review.googlesource.com/131635
Run-TryBot: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

cloudflare/go,nawawi/go,golang/go,cloudflare/go,nawawi/go,cloudflare/go,akutz/go,akutz/go,josharian/go,CAFxX/go,CAFxX/go,CAFxX/go,nawawi/go,akutz/go,akutz/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,josharian/go,cloudflare/go,josharian/go,josharian/go,akutz/go,golang/go,CAFxX/go,nawawi/go,akutz/go,golang/go,CAFxX/go,golang/go,CAFxX/go,golang/go,nawawi/go,golang/go,nawawi/go,cloudflare/go,akutz/go,cloudflare/go,nawawi/go,josharian/go,josharian/go,josharian/go,golang/go,josharian/go,golang/go,cloudflare/go,CAFxX/go