Issue with version 2 requests

[StefanSiebert]

Hello,

starting with version 1.0.7, http client caching was added and the default version string has changed from empty to 2.0
This will bring up the following exception for version 2 requests like adding a contact to a group (AddContactToGroup).

Microsoft.Skype.UCWA.Models.MethodNotAllowedException: The request isn't supported.
at async Task Microsoft.Skype.UCWA.Services.HttpService.HandleError(HttpResponseMessage response)
at async Task Microsoft.Skype.UCWA.Services.HttpService.ExecuteHttpCallAndRetry(Func<CancellationToken, Task> httpRequest, Func<HttpResponseMessage, T> deserializationHandler, CancellationToken cancellationToken)
at async Task Microsoft.Skype.UCWA.Services.HttpService.Post(string uri, object body, CancellationToken cancellationToken, string version, bool anonymous)
at async Task Microsoft.Skype.UCWA.UCWAClient.AddContactToGroup(string sip, string groupId, CancellationToken cancellationToken)

I have found out that the version string 2.0 has to be changed to 2 or it will be ignored. However, version 1 requests won't work then.
Changing the version back to an empty string and splitting the client caching also by version fixed the problem for me.

Thanks,

Stefan

[kenakamu]

Great. Could you craft PR for this one, please?