tools: enable no-extra-parens in ESLint

Enable `no-extra-parens`. This rule restricts the use of parentheses to
only where they are necessary. It is set to be restricted to report only
function expressions.

PR-URL: nodejs#5512
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

.eslintrc

@@ -14,6 +14,7 @@ rules:
   no-empty-character-class: 2
   no-ex-assign: 2
   no-extra-boolean-cast : 2
+  no-extra-parens: [2, "functions"]
   no-extra-semi: 2
   no-func-assign: 2
   no-invalid-regexp: 2

test/parallel/test-util-inspect.js

@@ -640,7 +640,7 @@ checkAlignment(new Map(big_array.map(function(y) { return [y, null]; })));
 }
 
 {
-  const x = new (function() {});
+  const x = new function() {};
   assert.equal(util.inspect(x), '{}');
 }