Update pug. Fix #631 (#632)

* Update pub. Fix #631

* pin dependency

Author: steren

appengine/static-files/package.json

@@ -22,7 +22,7 @@
   },
   "dependencies": {
     "express": "4.16.2",
-    "pug": "2.0.0"
+    "pug": "2.0.3"
   },
   "devDependencies": {
     "@google-cloud/nodejs-repo-tools": "2.2.1"