update changelog for April 2018 release
update changelog for April 2018 release

OfficeDev/PnP-Tools,PaoloPia/PnP-Tools,jansenbe/PnP-Tools,PaoloPia/PnP-Tools,OfficeDev/PnP-Tools,PaoloPia/PnP-Tools,Laul0/PnP-Tools,jansenbe/PnP-Tools,Laul0/PnP-Tools,OfficeDev/PnP-Tools,Laul0/PnP-Tools,jansenbe/PnP-Tools