Fix use of head

scripts/patch-tool

@@ -83,7 +83,7 @@ unpack_pkg() {
     local pkg=$1
     pushd packages
     cabal unpack --pristine $pkg
-    local pkg_dir="$(ls -d $pkg* | head)"
+    local pkg_dir="$(ls -d $pkg* | head -n 1)"
     if [ -z "$pkg_dir" ]; then
         echo "failed to unpack $pkg"
         exit 1