Changing PubgGameMode to String

[GavinPower747]

Due to the returns for the game mode no longer being limited to the documented values starting with Version 1.8.0 the GameMode value on the PubgMatch will no longer be an Enum and going forward will be a string.

I'm going to create an issue on the documentation repo to get a few things clarified if this is an issue and the API is supposed to be returning a limited amount of values as documented or get them to update their documentation. If this is an error the Enum will return otherwise, we'll be going with a string from now on.

[GavinPower747]

https://www.nuget.org/packages/Pubg-DotNet/1.8.0

First version with the string has been launched