dockerdeb: fix incorrect number of shifts stable

dockerdeb: fix incorrect number of shifts

From the comment, it appears that the original intent was to remove the first
two arguments, so this patch does just that.

--- a/contrib/dockerdeb	Thu Apr 21 10:11:20 2016 -0400
+++ b/contrib/dockerdeb	Sat Apr 23 12:47:39 2016 -0700
@@ -11,7 +11,7 @@
 DISTID="$1"
 CODENAME="$2"
 PLATFORM="$1-$2"
-shift # extra params are passed to build process
+shift; shift # extra params are passed to build process
 
 OUTPUTDIR=${OUTPUTDIR:=$ROOTDIR/packages/$PLATFORM}