Use retina logo size.

Author: dgraham

_layouts/default.html

@@ -16,7 +16,7 @@
 
     <ul class="row menu">
       <li class="col-xs-12 col-md-4">
-        <a href="index.html"><img class="img-responsive" src="logos/rust-logo-128x128-blk-v2.png" height="128" width="128" alt="Rust logo" /></a>
+        <a href="index.html"><img class="img-responsive" src="logos/rust-logo-256x256-blk.png" height="128" width="128" alt="Rust logo" /></a>
       </li>
       <li class="col-xs-4 col-md-2"><h2>Docs (Nightly)</h2>
         <ul>