Bump version to 1.18.8

debian/changelog

@@ -1,3 +1,9 @@
+dpkg (1.18.8) UNRELEASED; urgency=medium
+
+  *
+
+ -- Guillem Jover <guillem@debian.org>  Mon, 09 May 2016 05:10:36 +0200
+
 dpkg (1.18.7) unstable; urgency=medium
 
   [ Guillem Jover ]