Use current exe's icon as default window icon.
Use current exe's icon as default window icon.

Fixes atom/atom-shell#863.

brave/brightray,lakshmi-srinivas/brightray,bbondy/brightray,atom/brightray,bbondy/brightray,lakshmi-srinivas/brightray,tejaspathak/brightray,lakshmi-srinivas/brightray,tejaspathak/brightray,deepak1556/brightray,brave/brightray,deepak1556/brightray,atom/brightray