After migrated the Project, you have to Upgrade the project then only it will change from V11 to V12.
Upgrade Steps :-
1) Open the Project after migration
2) Select Project
3) click on "Upgrade"
Now you can see your project is upgraded to V12
-> upgrade your project from v11 to v12 (.ap11 will change to .ap12) or
-> continue to work with v11 project (.ap11) in compatibility mode