Fix default avatar not showing up in network graph

Closes https://github.com/gitlabhq/gitlabhq/issues/9657

CHANGELOG

@@ -11,6 +11,7 @@ v 8.1.0 (unreleased)
   - Remove "Continuous Integration" page from dashboard
 v 8.0.2 (unreleased)
+  - Fix default avatar not rendering in network graph (Stan Hu)
   - Skip check_initd_configured_correctly on omnibus installs
   - Prevent double-prefixing of help page paths
   - Clarify confirmation text on user deletion

app/views/projects/network/show.json.erb

@@ -9,7 +9,7 @@
         author: {
           name: c.author_name,
           email: c.author_email,
-          icon: avatar_icon(c.author_email, 20)
+          icon: image_path(avatar_icon(c.author_email, 20))
         },
         time: c.time,
         space: c.spaces.first,