Translate push validation error title with gettext.

Fixes #4447

Author: Peter Giacomo Lombardo

app/views/pushes/_error.html.erb

@@ -1,6 +1,6 @@
 <% if push.errors.any? %>
     <div class="alert alert-danger">
-        <div><%= pluralize(push.errors.count, "error") %> prohibited this push from being saved:</div>
+        <div><%= n_("%{count} error prohibited this push from being saved:", "%{count} errors prohibited this push from being saved:", push.errors.count) % { count: push.errors.count } %></div>
 
         <ul>
         <% push.errors.full_messages.each do |error| %>