Correct WiMi5 header id.

Review URL: https://codereview.chromium.org/1027853002

Cr-Commit-Position: refs/heads/master@{#321599}

chrome/common/extensions/docs/templates/articles/game_engines.html

@@ -37,7 +37,7 @@ package into a Chrome App. See:
 </p>
 
 
-<h2 id="playcanvas">WiMi5</h2>
+<h2 id="WiMi5">WiMi5</h2>
 <p>
 <a href="http://wimi5.com">http://wimi5.com</a>
 </p>