Update controls_screen.dart

Altered the control screen portion of the tutorial to display w a s d controls in the same order as the arrow controls.
Merge branch 'master' of https://github.com/Draco24/BeerRun into dev-movement
Merge pull request #34 from Draco24/master

Update controls_screen.dart
Merge branch 'master' of https://github.com/morendi/BeerRun into dev-movement