test.bash: update to go1.10.5 and go1.11.2

Change-Id: Ie62569d8544e262689dced53e9701859871962d9
Reviewed-on: https://go-review.googlesource.com/c/150076
Reviewed-by: Andrew Bonventre <andybons@golang.org>
Reviewed-by: Herbie Ong <herbie@google.com>

test.bash

@@ -37,8 +37,8 @@ mkdir -p $PROTOBUF_DIR/src/include
 ln -s ../google $PROTOBUF_DIR/src/include/google
 
 # Download each Go toolchain version.
-GO_LATEST=go1.11.1
-GO_VERSIONS=(go1.9.7 go1.10.4 $GO_LATEST)
+GO_LATEST=go1.11.2
+GO_VERSIONS=(go1.9.7 go1.10.5 $GO_LATEST)
 for GO_VERSION in ${GO_VERSIONS[@]}; do
 	if [ ! -d $GO_VERSION ]; then
 		print "download $GO_VERSION"