Test exchange - use public dummy http server (#630)

* don't use google

* use other url

protocol/daemons/pricefeed/client/price_function/test_volatile_exchange/exchange_query_details.go

@@ -22,7 +22,7 @@ var (
 	}
 	TestVolatileExchangeDetails = types.ExchangeQueryDetails{
 		Exchange:      exchange_common.EXCHANGE_ID_TEST_VOLATILE_EXCHANGE,
-		Url:           "https://www.google.com/",
+		Url:           "https://jsonplaceholder.typicode.com/users",
 		PriceFunction: VolatileExchangePriceFunction,
 		IsMultiMarket: false,
 	}