Disallow assigning to imported bindings (no-import-assign)

Fixes: standard/standard#1412

Author: feross

eslintrc.json

@@ -112,6 +112,7 @@
     "no-func-assign": "error",
     "no-global-assign": "error",
     "no-implied-eval": "error",
+    "no-import-assign": "error",
     "no-invalid-regexp": "error",
     "no-irregular-whitespace": "error",
     "no-iterator": "error",