dev_tool example has wrong import

## Bevy version
0.16.0

## What you did
Copy paste example from https://github.com/bevyengine/bevy/blob/latest/examples/dev_tools/fps_overlay.rs

## What went wrong
Failed to compile because the import is wrong.

- what were you expecting?
it to compile
- what actually happened?
error[E0433]: failed to resolve: could not find `dev_tools` in `bevy`

Open examples/dev_tools/fps_overlay.rs and inspect the import reported by the Bevy 0.16.0 compiler error. Run or compile the example after correcting the import, and consider the issue done when the example builds successfully.

Written by the indexing model from the issue text.