menu: Fix Zoom In shortcut.

This is a temporary fix. Ideally, 'CmdOrCtrl+Plus' works on all
the platforms but because of electron/electron#6731
it converts accelerator to 'Ctrl+Shift+Plus'.

Author: akashnimare

app/main/menu.js

@@ -54,7 +54,7 @@ class AppMenu {
 			role: 'togglefullscreen'
 		}, {
 			label: 'Zoom In',
-			accelerator: 'CommandOrControl+Plus',
+			accelerator: process.platform === 'darwin' ? 'Command+Plus' : 'Control+=',
 			click(item, focusedWindow) {
 				if (focusedWindow) {
 					AppMenu.sendAction('zoomIn');