code: function ContactsGroupsMembersGet(options, groupId, contactId) {
      ActionAbstract.call(this, options);
      this._groupId = groupId;
      this._contactId = contactId;
  }
docs: check whether contact is in group
  @see http://dev.smsapi.pl/#!/contacts%2Fgroups/contactsGet
  @param {Object} options
  @param {String} groupId
  @param {String} contactId
  @extends ActionAbstract
  @constructor