Make faster ProcessFeedService (#3080)

* Add index accounts on uri.

* Remove a blank line.

db/migrate/20170516072309_add_index_accounts_on_uri.rb

@@ -0,0 +1,5 @@
+class AddIndexAccountsOnUri < ActiveRecord::Migration[5.0]
+  def change
+    add_index :accounts, :uri
+  end
+end