Building on the scripts we released in June 2016 for DL migration, you can now migrate a distribution group to an Office 365 group directly from the Exchange Admin Center with one click. This feature is rolling out over the next few weeks. More information in this article.
In my opinion this is not migrating but just converting/ updating a DL (which is already located in Office 365) to O365 Group. When migrating a DL from on-prem to Office 365 (Group), that is what I call migrating, but that cannot be easily done.