Change example posts dates to be 3 years newer

No need to trick people into thinking Hakyll is dated when it is not ;)

hakyll.cabal

@@ -42,10 +42,10 @@ Build-Type:    Simple
 Data-Dir:      data
 
 Data-files:
-  example/posts/2012-11-28-carpe-diem.markdown
-  example/posts/2012-10-07-rosa-rosa-rosam.markdown
-  example/posts/2012-12-07-tu-quoque.markdown
-  example/posts/2012-08-12-spqr.markdown
+  example/posts/2015-11-28-carpe-diem.markdown
+  example/posts/2015-10-07-rosa-rosa-rosam.markdown
+  example/posts/2015-12-07-tu-quoque.markdown
+  example/posts/2015-08-12-spqr.markdown
   example/site.hs
   example/images/haskell-logo.png
   example/templates/post-list.html