fix teaser image link

Former-commit-id: ed88535f40b6247c8e9d2fe032ddfabee57ad1ba

README.md

@@ -1,7 +1,7 @@
 # libigl - A simple C++ geometry processing library
 [![Build Status](https://travis-ci.org/libigl/libigl.svg?branch=master)](https://travis-ci.org/libigl/libigl)
 [![Build status](https://ci.appveyor.com/api/projects/status/mf3t9rnhco0vhly8/branch/master?svg=true)](https://ci.appveyor.com/project/danielepanozzo/libigl-6hjk1/branch/master)
-![](libigl-teaser.png)
+![](https://github.com/libigl/libigl/raw/5ff6387765fa85ca46f1a6222728e35e2b8b8961/libigl-teaser.png)
 
 <https://github.com/libigl/libigl/>