tools: edit .eslintrc.js for minor maintainability improvements

* Add a comment explaining the Module._findPath() hacks so that someone
  else doesn't do what I do and try to remove them because they seem
  unnecessary for `make lint` and friends.
* Add a trailing comma for consistency with the rest of the file.

PR-URL: #27789
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Gus Caplan <me@gus.host>

.eslintrc.js

@@ -8,6 +8,10 @@ const path = require('path');
 const NodePlugin = require('./tools/node_modules/eslint-plugin-node-core');
 NodePlugin.RULES_DIR = path.resolve(__dirname, 'tools', 'eslint-rules');
 
+// The Module._findPath() monkeypatching is to make it so that ESLint will work
+// if invoked by a globally-installed ESLint or ESLint installed elsewhere
+// rather than the one we ship. This makes it possible for IDEs to lint files
+// with our rules while people edit them.
 const ModuleFindPath = Module._findPath;
 const hacks = [
   'eslint-plugin-node-core',
@@ -236,7 +240,7 @@ module.exports = {
       {
         selector: "CallExpression[callee.property.name='strictEqual'][arguments.0.type='Literal']:not([arguments.1.type='Literal']):not([arguments.1.type='ObjectExpression']):not([arguments.1.type='ArrayExpression']):not([arguments.1.type='UnaryExpression'])",
         message: 'The first argument should be the `actual`, not the `expected` value.',
-      }
+      },
     ],
     /* eslint-enable max-len */
     'no-return-await': 'error',