NCBC-381: Ensure that Nuget installs Newtonsoft.NET 4.5.11

If this is not specified in the .nuspec file, Nuget will attempt to
install the lastest version 6.0.0 which is not compatible with view
calls using 1.3.2 version of the Couchbase .NET SDK. These incompatible
issues will be resolved in a future release, likely 1.3.3

Change-Id: Ia5f2cc871a00f207f07e489b5e8d13b3dcc8a149
Reviewed-on: http://review.couchbase.org/33219
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>