Update Migration Guide.md

Maybe this will save someone else the 30 minute debug
Merge pull request #639 from BorisKozo/patch-1

Update Migration Guide.md
You can now create multiple blank layers in a Tilemap.
Tilemap fixes.
New build files with tilemap callback fixes in.
Timer objects incorrectly set the first tick value on events if you added the events prior to starting them.
All Timer events are now increased by the game time on start.
Moved the PhysicsEditor plugin to the resources folder.
Fixed small typos in the README.
Updated docs to 2.0.1.
Tutorial updated for Phaser 2
Tween.generateData would enter an eternal loop if the total resulted in a float. Now wrapped in Math.floor.
Line.fromSprite now sets "fromCenter" to false by default as Sprite.center is deprecated in 2.x. Documentation and Examples updated to reflect this.
Fix .jshintrc whitespace.
Remove unnecessary .jshintrc flags.
Remove jshint options that contradict coding style.
Run jshint as part of build process.
Trim trailing whitespace.
Fix jshint issues in src/tilemap
Fix jshint issues in src/particles/arcade