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-3.3, inspired by similar pages for recent GMP releases.
-    [Last updated 2016-05-04]</p>
+    [Last updated 2016-09-06]</p>
   <p class='should'>
     This really ought to be done before release
   </p>