[CoinbasePro] Change "after" param to String

[piechu111]

There is a ledger method in CoinbasePro interface and it has a Integer startingOrderId parameter. I think it should be a String because in some case orderId is greater then maxiumum value of Integer. Additionally, CoinbasePro documentation says that this parameter should be a String -> https://docs.cloud.coinbase.com/exchange/reference/exchangerestapi_getaccountledger

  @Path("accounts/{account_id}/ledger")
  @Consumes(MediaType.APPLICATION_JSON)
  List<Map<?, ?>> ledger(
      @HeaderParam("CB-ACCESS-KEY") String apiKey,
      @HeaderParam("CB-ACCESS-SIGN") ParamsDigest signer,
      @HeaderParam("CB-ACCESS-TIMESTAMP") long timestamp,
      @HeaderParam("CB-ACCESS-PASSPHRASE") String passphrase,
      @PathParam("account_id") String accountId,
      @QueryParam("after") Integer startingOrderId)  //should be a String
      throws CoinbaseProException, IOException;

What do you think about this change? Please consider it.