fix: update settlePlan field type to support null values (#64)

Author: gryumov

Project.toml

@@ -1,6 +1,6 @@
 name = "CryptoExchangeAPIs"
 uuid = "5e3d4798-c815-4641-85e1-deed530626d3"
-version = "0.33.0"
+version = "0.33.1"
 
 [deps]
 Base64 = "2a0f44e3-6c83-55bd-87e4-b1978d98bd5f"

src/Binance/USDMFutures/API/ExchangeInfo.jl

@@ -55,7 +55,7 @@ struct Symbols <: BinanceData
     quoteAsset::String
     quotePrecision::Int64
     requiredMarginPercent::Float64
-    settlePlan::Int64
+    settlePlan::Union{Nothing,Int64}
     status::String
     symbol::String
     timeInForce::Vector{String}
@@ -102,7 +102,7 @@ Current exchange trading rules and symbol information.
 using Serde
 using CryptoExchangeAPIs.Binance
 
-result = Binance.USDMFutures.exchange_info() 
+result = Binance.USDMFutures.exchange_info()
 
 to_pretty_json(result.result)
 ```