Import of `flask._compat` fails with Flask 2.0

In the very recent 2.0 release of Flask 2.0, they dropped support for Python < 3.6.
This includes the removal of the `flask._compat` module (https://github.com/pallets/flask/commit/662c245795c7cbb5dbd657a2d707c62c16770c18)
Thus, the following import won't work anymore: https://github.com/klen/Flask-Collect/blob/develop/flask_collect/collect.py#L7

Open flask_collect/collect.py at the import on line 7 and compare it with Flask 2.0's removal of flask._compat described in the issue. Confirm the failure with Flask 2.0, then update the compatibility handling so the module imports successfully and verify the static-file collection path still works.

Written by the indexing model from the issue text.