fix test expected error message

Author: akerekes

test/test_server.rb

@@ -203,7 +203,7 @@ def query_server_with_retry server
     end
 
     assert_equal "400", response.code
-    assert_match /unexpected token/, response.body
+    assert_match "/unexpected token/", response.body
     assert_equal "text/plain; charset=utf-8", response["Content-Type"]
   end