renovate: Add post-update command to tidy modules (#128)

Author: echarrod

renovate.json

@@ -4,5 +4,11 @@
   ],
   "additionalReviewers": [
     "andrewwormald"
-  ]
+  ],
+  "postUpgradeTasks": {
+    "commands": [
+      "find . -name \"go.mod\" -type f -exec dirname {} \\; | while read dir; do echo \"Running go mod tidy in $dir\"; cd \"$dir\" && go mod tidy && cd - > /dev/null; done"
+    ],
+    "fileFilters": ["**/go.mod", "**/go.sum"]
+  }
 }