update index.html to match README.md

Former-commit-id: 9a080e349cb0813b330f6bdf36960899b029b628

index.html

@@ -16,7 +16,7 @@
 
 <figure>
 <img src="libigl-teaser.png" alt="" />
-</figure>
+<figcaption></figcaption></figure>
 
 <p><a href="https://github.com/libigl/libigl/">https://github.com/libigl/libigl/</a></p>