delay closing window on iOS to prevent crash

Added a 750ms delay before attempting to close pop up on iOS to give
the email dialog time to close out. tried several values and got the
error below on ~500ms and below. tested on iPad 3, 5s & simulator
successfully

Dismissing a view controller when it is not the top presented view
controller. Will probably crash now.

attempt to dismiss modal view controller whose view does not currently
appear. self = <TiViewController: 0xcf90a30> modalViewController =
<MFMailComposeViewController: 0xd043c50>

attempt to dismiss modal view controller whose view does not currently
appear. self = <TiRootViewController: 0xd2243e0> modalViewController =
<TiViewController: 0xcf90a30>
Merge pull request #11 from n3wc/master

delay closing window on iOS to prevent crash