Fix dir in Plumb cmd

If the clipboard contains a filename or git hash (e.g. copied on a
website) this makes it possible to open it with the Plumb cmd if the
focused win is a buf in the project root (e.g. ^agit or guide).

Author: xyb3rt

bin/Plumb

@@ -1,2 +1,3 @@
-#!/bin/sh
+#!/bin/sh -e
+cd "$ACMEVIMDIR"
 exec avim -p "$(xsel -bo)"