Fix xmlns:media namespacing for atom feeds

app/views/dashboard/issues.atom.builder

 xml.instruct!
-xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlnsmedia" => "http://search.yahoo.com/mrss/" do
+xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlns:media" => "http://search.yahoo.com/mrss/" do
   xml.title   "#{current_user.name} issues"
   xml.link    href: issues_dashboard_url(:atom, private_token: current_user.private_token), rel: "self", type: "application/atom+xml"
   xml.link    href: issues_dashboard_url(private_token: current_user.private_token), rel: "alternate", type: "text/html"

app/views/dashboard/show.atom.builder

 xml.instruct!
-xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlnsmedia" => "http://search.yahoo.com/mrss/" do
+xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlns:media" => "http://search.yahoo.com/mrss/" do
   xml.title   "Dashboard feed#{" - #{current_user.name}" if current_user.name.present?}"
   xml.link    href: dashboard_url(:atom), rel: "self", type: "application/atom+xml"
   xml.link    href: dashboard_url, rel: "alternate", type: "text/html"

app/views/groups/show.atom.builder

 xml.instruct!
-xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlnsmedia" => "http://search.yahoo.com/mrss/" do
+xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlns:media" => "http://search.yahoo.com/mrss/" do
   xml.title   "Group feed - #{@group.name}"
   xml.link    href: group_path(@group, :atom), rel: "self", type: "application/atom+xml"
   xml.link    href: group_path(@group), rel: "alternate", type: "text/html"

app/views/users/show.atom.builder

 xml.instruct!
-xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlnsmedia" => "http://search.yahoo.com/mrss/" do
+xml.feed "xmlns" => "http://www.w3.org/2005/Atom", "xmlns:media" => "http://search.yahoo.com/mrss/" do
   xml.title   "Activity feed for #{@user.name}"
   xml.link    href: user_url(@user, :atom), rel: "self", type: "application/atom+xml"
   xml.link    href: user_url(@user), rel: "alternate", type: "text/html"