replaced missing faq link

lib/failure.sh

@@ -57,7 +57,7 @@ warn_node_engine() {
 warn_prebuilt_modules() {
   local build_dir=${1:-}
   if [ -e "$build_dir/node_modules" ]; then
-    warning "node_modules checked into source control" "https://docs.npmjs.com/misc/faq#should-i-check-my-node-modules-folder-into-git"
+    warning "node_modules checked into source control" "https://blog.heroku.com/node-habits-2016#9-only-git-the-important-bits"
   fi
 }