Use avatar_icon_for_email for commits.

We need to keep the email lookup as we want to fall back to displaying
the gravatar result for a given email if the user does not exist.

app/views/projects/commits/_commit.atom.builder

@@ -3,7 +3,7 @@ xml.entry do
   xml.link    href: project_commit_url(@project, id: commit.id)
   xml.title   truncate(commit.title, length: 80, escape: false)
   xml.updated commit.committed_date.xmlschema
-  xml.media   :thumbnail, width: "40", height: "40", url: image_url(avatar_icon(commit.author_email))
+  xml.media   :thumbnail, width: "40", height: "40", url: image_url(avatar_icon_for_email(commit.author_email))
 
   xml.author do |author|
     xml.name commit.author_name

app/views/projects/repositories/_feed.html.haml

@@ -11,7 +11,7 @@
     %div
       = link_to project_commits_path(@project, commit.id) do
         %code= commit.short_id
-      = image_tag avatar_icon(commit.author_email), class: "", width: 16, alt: ''
+      = image_tag avatar_icon_for_email(commit.author_email), class: "", width: 16, alt: ''
       = markdown(truncate(commit.title, length: 40), pipeline: :single_line, author: commit.author)
   %td
     %span.pull-right.cgray