Update to node 6.11.1

Fixes a DDoS issue in node

https://nodejs.org/en/blog/vulnerability/july-2017-security-releases/

scripts/createReleaseTarball

@@ -31,8 +31,8 @@ if ! $(cd "${SOURCE_DIR}" && git diff --exit-code >/dev/null); then
     exit 1
 fi
 
-if [[ "$(node --version)" != "v6.9.2" ]]; then
-    echo "This script requires node 6.9.2"
+if [[ "$(node --version)" != "v6.11.1" ]]; then
+    echo "This script requires node 6.11.1"
     exit 1
 fi