Update cyg-get

Update cyg-get to be able to run straight after installing cyg-get, if you don't close and reopen Powershell after installing cyg-get (spawning a new Powershell within doesn't work), cyg-get doesn't work. This will make cyg-get find the cygwinsetup.exe without restarting Powershell.
Update cyg-get.ps1

I have tested this change and it works. No need to fiddle with changing of directories. Let me know if you have any concerns. 
Also thank you for helping me through this too, my first open-source contribution ;D
Merge pull request #21 from RyanCarrier/patch-1

Update cyg-get