test.bash: use go1.11

Change-Id: Ia0b76eba666738e477d3a7403aee2dc16dd8e0f9
Reviewed-on: https://go-review.googlesource.com/131344
Reviewed-by: Herbie Ong <herbie@google.com>

test.bash

@@ -33,7 +33,7 @@ register_binary conformance-test-runner $PROTOBUF_DIR/conformance/conformance-te
 register_binary protoc $PROTOBUF_DIR/src/protoc
 
 # Download each Go toolchain version.
-GO_LATEST=go1.11rc2
+GO_LATEST=go1.11
 GO_VERSIONS=(go1.10.3 $GO_LATEST)
 for GO_VERSION in ${GO_VERSIONS[@]}; do
 	if [ ! -d $GO_VERSION ]; then