chore(doc-gen): add - var ... to jade variable declarations

Harp 0.17 requires that jade variables are declared correctly

Closes angular#3325

Author: petebacondarwin

docs/angular.io-package/templates/module.template.html

@@ -7,7 +7,7 @@
 ul
   for page, slug in public.docs[current.path[1]][current.path[2]][current.path[3]][current.path[4]]._data
     if slug != 'index'
-      url = "/docs/" + current.path[1] + "/" + current.path[2] + "/" + current.path[3] + "/" + current.path[4] + "/" + slug + ".html"
+      - var url = "/docs/" + current.path[1] + "/" + current.path[2] + "/" + current.path[3] + "/" + current.path[4] + "/" + slug + ".html"
 
       li.c8
         != partial("../../../../../_includes/_hover-card", {name: page.title, url: url })