Fix PlayerToggleFlightEvent

Currently used .f()
https://github.com/SpigotMC/mc-dev/blob/master/net/minecraft/server/PacketPlayInAbilities.java#L90

Which returns canInstantlyBuild boolean

Needs to be changed to .d()
https://github.com/SpigotMC/mc-dev/blob/master/net/minecraft/server/PacketPlayInAbilities.java#L74

Which returns isFlying