Fix Jenkins not being able to deal with `sh` in `/freetz`.

Jenkinsfile

@@ -10,11 +10,12 @@ node("linux && amd64 && docker") {
       """
     }
 
-    dir("/freetz") {
     sh """
-      cd ${pwd()}
+    cd /freetz
     su freetz -c \"sh -c 'umask 0022 && make oldconfig && make'\"
     """
+
+    dir("/freetz") {
       archive "images/**,outboard/**"
     }
   }