Don't use zuul_work_dir in post-stackviz

The stackviz publish job fails with
"The task includes an option with an undefined variable. The error was:
'zuul_work_dir' is undefined"

Use zuul.project.src.dir instead of zuul_work_dir.

Change-Id: I443d0b4bfb30a06d68321d402802ae1b433bab6b

playbooks/javascript/post-stackviz.yaml

@@ -23,13 +23,13 @@
       synchronize:
         dest: "{{ zuul.executor.work_root }}/artifacts/"
         mode: pull
-        src: "{{ zuul_work_dir }}/dist/"
+        src: "{{ zuul.project.src_dir }}/dist/"
         verify_host: true
 
     - name: Find tarball tarball
       find:
         file_type: file
-        paths: "{{ zuul_work_dir }}/dist/"
+        paths: "{{ zuul.project.src_dir }}/dist/"
         patterns: "*.tar.gz"
       register: result