Finally, the support for migrating Distribution list to Office 365 group comes to live through Office 365 Admin center. The introduction of Office 365 groups gives the next level for cloud first and mobile first agenda since it gives the rich collaboration experiences.
The office 365 group is the next generation type of group that replaces the function of a traditional distribution list, and it includes the benefits of a security group, along with many other rich collaboration that enables teams to come together and establish a single team identity and a single set of permissions across different Office 365 apps including Outlook, Planner, OneNote,OneDrive, Skype for Business, etc.
Using new DL migration option, you can now migrate a distribution group to an Office 365 group directly from the Exchange Admin Center.
For more details read this thread: https://network.office.com/t5/Exchange/Migrate-a-distribution-group-to-an-Office-365-group-with-one/m-p/4340/highlight/true#M81