Use short URL for png link (#22)

Author: ryanve

index.html

@@ -6,7 +6,7 @@
 <meta name="description" content="San Francisco bae color palette. Welcome to the bae.">
 <meta name="theme-color" content="#bae">
 
-<!-- images via https://github.com/s9a/bae/issues/5 -->
+<!-- https://git.io/bae_png -->
 <meta property="og:image" content="https://user-images.githubusercontent.com/949985/46566589-3e628280-c8d6-11e8-8492-3c3fceb6ac60.png">
 <meta property="og:image:alt" content="#bae">
 <meta property="og:image" content="https://user-images.githubusercontent.com/949985/46566565-dca21880-c8d5-11e8-8b82-677cec7a116c.png">