updateGroup 
          Update information about a group
Parameters
groupID 
The base64-encoded ID of the V2 group to update
groupUpdate 
The update to make to the group. This is done as a sealed class so that only one of the modification actions can be performed at once. See GroupUpdate for details and all possible update types.
Throws
if signald sends an error response or the incoming message is invalid
if the request to the socket fails