index: remove references to Python 2

Author: davvid

index.html

@@ -37,8 +37,8 @@
         is a sleek and powerful graphical user interface for
         <a href="https://git-scm.com/">Git</a>.
         <br>
-        Git Cola is <a href="license.html">free software</a> and written in
-        <a href="https://www.python.org/">Python</a> (v2 + v3).
+        Git Cola is <a href="license.html">free software</a>
+        and powered by Python and PyQt.
     </div>
 
     <div style="margin: 2em">