Update date.

misc/plan.html

@@ -14,7 +14,7 @@
   <h1> Nettle release plans </h1>
   <p> This is an attempt at defining a development target for
   Nettle-2.8, inspired by similar pages for recent GMP releases. [Last
-  updated 2014-01-27]</p>
+  updated 2014-03-28]</p>
   <p class='should'>
     This really ought to be done before release
   </p>