Call atom.show() from a setTimeout()

The window was previously flashing white if atom.show() was called
directly after window.startup()

Wrapping the call in a setTimeout with a zero delay seems to prevent
the white flash and the perceived amount of time to display the contents
appears to be the same.

src/window-bootstrap.coffee

@@ -5,5 +5,5 @@ require 'window'
 
 window.setUpEnvironment()
 window.startup()
-atom.show()
+setTimeout((-> atom.show()), 0)
 console.log "Load time: #{new Date().getTime() - date}"