MouseUp; fix bug with resizing panes
MouseUp; fix bug with resizing panes

from:
https://github.com/ravichugh/sketch-n-sketch/commit/1d2595888109ac285371712013c1b400e751b9f4

ravichugh/sketch-n-sketch,ravichugh/sketch-n-sketch,ravichugh/sketch-n-sketch,ravichugh/sketch-n-sketch,ravichugh/sketch-n-sketch,ravichugh/sketch-n-sketch