[scene2d] Added Tree#updateRootNodes.
[scene2d] Added Tree#updateRootNodes.

alex-dorokhov/libgdx,tommyettinger/libgdx,cypherdare/libgdx,MikkelTAndersen/libgdx,bladecoder/libgdx,MikkelTAndersen/libgdx,alex-dorokhov/libgdx,stinsonga/libgdx,Zomby2D/libgdx,libgdx/libgdx,stinsonga/libgdx,MikkelTAndersen/libgdx,MikkelTAndersen/libgdx,NathanSweet/libgdx,MikkelTAndersen/libgdx,tommyettinger/libgdx,libgdx/libgdx,bladecoder/libgdx,tommyettinger/libgdx,alex-dorokhov/libgdx,NathanSweet/libgdx,tommyettinger/libgdx,tommyettinger/libgdx,alex-dorokhov/libgdx,Zomby2D/libgdx,libgdx/libgdx,cypherdare/libgdx,cypherdare/libgdx,cypherdare/libgdx,stinsonga/libgdx,MikkelTAndersen/libgdx,alex-dorokhov/libgdx,MikkelTAndersen/libgdx,libgdx/libgdx,Zomby2D/libgdx,bladecoder/libgdx,bladecoder/libgdx,Zomby2D/libgdx,cypherdare/libgdx,stinsonga/libgdx,alex-dorokhov/libgdx,libgdx/libgdx,alex-dorokhov/libgdx,NathanSweet/libgdx,bladecoder/libgdx,NathanSweet/libgdx,Zomby2D/libgdx,stinsonga/libgdx,MikkelTAndersen/libgdx,NathanSweet/libgdx,alex-dorokhov/libgdx