cmd/go: close debug trace file

Change-Id: Ia83312e6b0448573d40fe9a58ab42cd0d8f8f44a
GitHub-Last-Rev: 30f462817b
GitHub-Pull-Request: golang/go#66436
Reviewed-on: https://go-review.googlesource.com/c/go/+/573215
Reviewed-by: David Chase <drchase@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Matloob <matloob@golang.org>

src/cmd/go/main.go

@@ -261,6 +261,7 @@ func invoke(cmd *base.Command, args []string) {
 		}
 		defer func() {
 			rtrace.Stop()
+			f.Close()
 		}()
 	}