doc: fix footer sizing

reduced to the minimal amount, any less shows a white bar.

Semver: patch
PR-URL: https://github.com/iojs/io.js/pull/860
Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>

doc/api_assets/style.css

@@ -393,7 +393,7 @@ span.type {
 
 #footer {
   padding: 0;
-  min-height: 300px;
+  min-height: 24px;
   background: #333;
   color: white;
 }