Update logo link to point to datahaskell.org

Author: mchav

_includes/header.html

@@ -1,5 +1,5 @@
 <header id="header">
-  <h1 id="logo"><a href="index.html">data<span>Haskell</span></a></h1>
+  <h1 id="logo"><a href="https://datahaskell.org/index.html">data<span>Haskell</span></a></h1>
   <nav id="nav">
     <!-- Header -->
     <ul>