Zooming in or Out in Sketch App for Mac using command + space bar (Keyboard Combination) triggers spotlight!
I have actually came across a completely different solution. You must be knowing about hot corners in which if you point the cursor to any corner of the screen a particular process takes place so now I have turned it on for the launchpad and now I can happily zoom in or zoom out in Sketch! 

Hot corners can be accessed either from the mission control screen under system preferences or from the screensaver screen also under the system preferences!