Fix repl.it in old blog post

blog/2016-12-15-2016-in-jest.md

@@ -19,7 +19,9 @@ I'd like to deeply thank all the people that have [contributed to Jest this year
 
 Amjad Massad [built a Jest container](https://repl.it/languages/jest) so you can now try out Jest directly in the browser. You can use it from now on when creating GitHub issues which should help troubleshoot problems more quickly. Amjad and Haya are building [repl.it](http://repl.it/) to democratize programming by building powerful yet simple tools and platforms for educators, learners, and developers. They are also [hiring talented engineers](https://repl.it/site/jobs)!
 
-<iframe class="jest-repl" src="https://repl.it/languages/jest?lite=true"></iframe>
+<div class="jest-repl">
+  <iframe src="https://repl.it/languages/jest?lite=true"></iframe>
+</div>
 
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