.eslintrc.json: Enable require-atomic-updates rule

Although Promises aren't support by Qt Script anyway, some scripts in
the res/controllers directory are using Promises anyway (i.e. the Novation
Launchpad scripts). So in any case it doesn't hurt to enable this rule.

.eslintrc.json

@@ -10,7 +10,7 @@
     "eqeqeq": ["error", "always"],
     "camelcase": "error",
     "dot-location": "off",
-    "require-atomic-updates": "off"
+    "require-atomic-updates": "error"
   },
   "globals": {
     "console": "writable",