Change <pre name=code> tags to <pre><code> and adjust CSS

Author: Gregory Cox

docs/a-fistful-of-monads.html

@@ -58,7 +58,7 @@ img.center {
     margin:10px auto 25px auto;
     display:block;
 }
-pre.code {
+pre > code {
     color:white;
     /*background-color:#522812;*/
     background-color:black;