Build: Enable strict eqeqeq rule always

Previously, the inherited config from eslint-config-standard enabled
the rule, but it sets an exemption for loose equality with null [1].

The instance in html.js will be fixed in a separate patch since that
actually obscured a bug.

[0]: https://eslint.org/docs/latest/rules/eqeqeq
[1]: https://github.com/standard/eslint-config-standard/blob/v17.1.0/.eslintrc.json#L61

.eslintrc.base.js

@@ -19,6 +19,7 @@ const config = Object.assign(standard, {
     'prefer-const': 'off',
     'prefer-promise-reject-errors': 'off',
     // extra
+    eqeqeq: ['error'],
     'no-unused-vars': ['error', { args: 'all', argsIgnorePattern: '^_' }]
   })
 });

src/html-reporter/html.js

@@ -216,6 +216,7 @@ const stats = {
           }
         } else {
           let test;
+          // eslint-disable-next-line eqeqeq
           while ((test = hiddenTests.pop()) != null) {
             tests.appendChild(test);
           }

src/test.js

@@ -772,7 +772,7 @@ Test.prototype = {
   },
 
   resolvePromise: function (promise, phase) {
-    if (promise != null) {
+    if (promise !== undefined && promise !== null) {
       const test = this;
       const then = promise.then;
       if (typeof then === 'function') {