cmd/go: use hg repo for code.google.com shutdown check

svn dies due to not being able to validate the googlecode.com certificate.
hg does not even attempt to validate it.

Fixes #11806.

Change-Id: I84ced5aa84bb1e4a4cdb2254f2d08a64a1ef23f6
Reviewed-on: https://go-review.googlesource.com/12558
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/cmd/go/go_test.go

@@ -2094,7 +2094,7 @@ func TestIssue10193(t *testing.T) {
 	tg.parallel()
 	tg.tempDir("src")
 	tg.setenv("GOPATH", tg.path("."))
-	tg.runFail("get", "code.google.com/p/rsc-svn")
+	tg.runFail("get", "code.google.com/p/rsc/pdf")
 	tg.grepStderr("is shutting down", "missed warning about code.google.com")
 }