Fix minor errors in FlxTween documentation in handbook.
Fix minor errors in FlxTween documentation in handbook.

Doppp/flixel-docs,jcward/flixel-docs,Gama11/flixel-docs,flabbyfabby/flixel-docs,Gama11/flixel-docs,flabbyfabby/flixel-docs,flabbyfabby/flixel-docs,jcward/flixel-docs,Doppp/flixel-docs