Bittrex - changed type of field "Id" in DepositHistory struct (#419)

* Bittrex GetDepositHistory method return new DepositHistory struct type

* Id field of DepositHistory type changed to int64

* check exchange (exist and enabled) before calling methods on, to avoid program crashes

* Update bittrex_types.go

exchanges/bittrex/bittrex_types.go

@@ -215,7 +215,7 @@ type DepositHistory struct {
 	Success bool   `json:"success"`
 	Message string `json:"message"`
 	Result  []struct {
-		ID            string  `json:"Id"`
+		ID            int64   `json:"Id"`
 		Amount        float64 `json:"Amount"`
 		Currency      string  `json:"Currency"`
 		Confirmations int64   `json:"Confirmations"`