parse QuantityStepSize (base_increment) in Coinbase (DigitalRuby#715)

Author: vslee

src/ExchangeSharp/API/Exchanges/Coinbase/ExchangeCoinbaseAPI.cs

@@ -199,7 +199,8 @@ protected internal override async Task<IEnumerable<ExchangeMarket>> OnGetMarketS
 					IsActive = string.Equals(product["status"].ToStringInvariant(), "online", StringComparison.OrdinalIgnoreCase),
 					MinTradeSize = product["base_min_size"].ConvertInvariant<decimal>(),
 					MaxTradeSize = product["base_max_size"].ConvertInvariant<decimal>(),
-					PriceStepSize = product["quote_increment"].ConvertInvariant<decimal>()
+					PriceStepSize = product["quote_increment"].ConvertInvariant<decimal>(),
+					QuantityStepSize = product["base_increment"].ConvertInvariant<decimal>(),
 				};
 				markets.Add(market);
 			}