Docs: Fixed missing markdown codeblock closing

Closes gh-1930

Author: Francisc

lib/rules/require-object-keys-on-new-line.js

@@ -46,6 +46,7 @@
  *     b: 'b', c: 'c',
  *     d: 'd'
  * };
+ * ```
  */
 
 var assert = require('assert');