Fixes GetContractMultiplier

GetContractMultiplier was rounding contract multiplier incorrectly,
leading to an unsuccessful contract details request. E.g. LBR multiplier
is 27.5 and was converted to "28" instead of "27.5".

Instead of rounding all multipliers above 1, we will only round them if
the decimal part is zero.

QuantConnect.InteractiveBrokersBrokerage/InteractiveBrokersBrokerage.cs

@@ -4119,7 +4119,7 @@ public IEnumerable<Symbol> LookupSymbols(Symbol symbol, bool includeExpired, str
 
         private static string GetContractMultiplier(decimal contractMultiplier)
         {
-            if (contractMultiplier >= 1)
+            if (contractMultiplier % 1 == 0)
             {
                 // IB doesn't like 5000.0
                 return Convert.ToInt32(contractMultiplier).ToStringInvariant();