Update KeenClient.nuspec

updated all dependency versions to the latest versions (by May 26, 2014) to support Windows Phone 8.1
Update KeenClient.nuspec
Added Windows Phone 8.1 support

Here I have added the latest dependencies (by May 26th 2014) and added
the support for Windows Phone 8.1.
Merge branch 'master' of https://github.com/IshamMohamed/keen-sdk-net into IshamMohamed-master
Merge branch 'IshamMohamed-master' into release-0.2.0
updated nuget package