Update 04-flxgroup.html.md
Update 04-flxgroup.html.md

fix getFirstAvailable description
Gama11/flixel-docs,jcward/flixel-docs,Gama11/flixel-docs,jcward/flixel-docs,Doppp/flixel-docs,flabbyfabby/flixel-docs,flabbyfabby/flixel-docs,flabbyfabby/flixel-docs,Doppp/flixel-docs