Require strict equality

The guide dictates that [strict equality must be used](https://google.github.io/styleguide/jsguide.html#features-equality-checks) with an exception for `x == null`, which matches ESLint's `eqeqeq: 'smart'` behaviour.

index.js

@@ -87,7 +87,7 @@ module.exports = {
     // 'default-case': 'off',
     // 'dot-location': 'off',
     // 'dot-notation': 'off',
-    // 'eqeqeq': 'off',
+    'eqeqeq': ['error', 'smart'],
     'guard-for-in': 'error',
     // 'no-alert': 'off',
     'no-caller': 'error',