updates renovate to ignore old samples

Author: bshaffer

.github/renovate.json

@@ -3,5 +3,9 @@
     "config:base",
     ":preserveSemverRanges",
     ":rebaseStalePrs"
+  ],
+  "ignorePaths": [
+    "appengine/php55",
+    "appengine/flexible"
   ]
 }