Link newer ESLint rule (namely comma-dangle)

The "no-comma-dangle" rule was deprecated in favor or "comma-dangle" in
ESLint v1.0.

See http://eslint.org/docs/rules/no-comma-dangle.html,
http://eslint.org/docs/rules/comma-dangle, and line 4 of
packages/eslint-config-airbnb/rules/errors.js.

Author: strburst

README.md

@@ -1774,7 +1774,7 @@ Other Style Guides
 
   - [19.2](#19.2) <a name='19.2'></a> Additional trailing comma: **Yup.**
 
-    eslint rules: [`no-comma-dangle`](http://eslint.org/docs/rules/no-comma-dangle.html).
+    eslint rules: [`comma-dangle`](http://eslint.org/docs/rules/comma-dangle.html).
 
     > Why? This leads to cleaner git diffs. Also, transpilers like Babel will remove the additional trailing comma in the transpiled code which means you don't have to worry about the [trailing comma problem](es5/README.md#commas) in legacy browsers.