Update roadmap.md

[Ahmed-H-N]

Update roadmap, mark ExpansionTile as done (in flet-dev/flet#2140)

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}

[FeodorFitsner]

Roadmap will be updated as part of #177