Fix "NameError: undefined local variable or method `primary' for...

Fix "NameError: undefined local variable or method `primary' for #<ApplicationTests::ServerTest:0x000055df43b391d8>"

railties/test/application/server_test.rb

@@ -51,7 +51,7 @@ def teardown
           rails("restart")
 
           assert_output("Restarting", master)
-          assert_output("Listening", primary)
+          assert_output("Listening", master)
         ensure
           kill(pid) if pid
         end