correct a minor spelling mistake in the changelog

debian/changelog

@@ -8,7 +8,7 @@ apt (0.7.26~exp6) UNRELEASED; urgency=low
       that use round robin DNS)
     - support Original-Maintainer in RewritePackageOrder
     - enable cdrom autodetection via libudev by default
-    - show messsage about Vcs in use when apt-get source is run for
+    - show message about Vcs in use when apt-get source is run for
       packages maintained in a Vcs
     - better support transitional packages with mark auto-installed. 
       when the transitional package is in "oldlibs" the new package