Use defaults in renovate.json

Author: max-lobur

.github/renovate.json

@@ -11,7 +11,6 @@
   },
   "postUpgradeTasks": {
     "commands": ["make readme"],
-    "fileFilters": ["README.md"],
-    "executionMode": "update"
-  } 
+    "fileFilters": ["README.md"]
+  }
 }