Fix the order of receivers in the DotHelper specs

This should fix occasional build failure on CI.

spec/helpers/dot_helper_spec.rb

@@ -53,6 +53,11 @@ describe DotHelper do
         ]
         @foo.reload
         @bar2.reload
+
+        # Fix the order of receivers
+        @agents.each do |agent|
+          stub.proxy(agent).receivers { |orig| orig.order(:id) }
+        end
       end
 
       it "generates a DOT script" do