test.bash: use go1.11rc2

Change-Id: I5228fc8156a1a2800cab5b753f97dc542d520ba5
Reviewed-on: https://go-review.googlesource.com/131155
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=go1.11rc1
+GO_LATEST=go1.11rc2
 GO_VERSIONS=(go1.10.3 $GO_LATEST)
 for GO_VERSION in ${GO_VERSIONS[@]}; do
 	if [ ! -d $GO_VERSION ]; then