debian: Bump the version to ease upgrading from Debian

Debian SID has version 0.92-1 and we had 0.92. Bump it to 0.93.
diff --git a/debian/changelog b/debian/changelog
index 4326a14..a00671b 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,3 +1,9 @@
+openggsn (0.93) UNRELEASED; urgency=medium
+
+  * Bump version to ease upgrading from Debian SID.
+
+ -- Holger Hans Peter Freyther <holger@moiji-mobile.com>  Tue, 24 May 2016 22:53:16 +0200
+
 openggsn (0.92) precise; urgency=medium
 
   * Release 0.92