Disallow assignment to exports

Fixes: standard/standard#1400

Author: feross

eslintrc.json

@@ -227,6 +227,7 @@
 
     "node/handle-callback-err": ["error", "^(err|error)$" ],
     "node/no-deprecated-api": "error",
+    "node/no-exports-assign": "error",
     "node/no-new-require": "error",
     "node/no-path-concat": "error",
     "node/process-exit-as-throw": "error",