Give 0.2.5.5-alpha a release date

ChangeLog

@@ -1,4 +1,4 @@
-Changes in version 0.2.5.5-alpha - 2014-06-1?
+Changes in version 0.2.5.5-alpha - 2014-06-18
   Tor 0.2.5.5-alpha fixes a wide variety of remaining issues in the Tor
   0.2.5.x release series, including a couple of DoS issues, some
   performance regressions, a large number of bugs affecting the Linux