New google sign in update.

[AzadNezamdoust]

In google sign in SDK v 5+ there are some changes not made in the sample code also it is necessary to update it because google sign in SDK v -5 is using ui web view which is deprecated from iOS and gets rejected, meaning google sign in can't be used in iOS. Please give an update google. I am using google sign in for my iOS Unity app.

[daerxi]

#126
use this branch, change the content in your project following the one he did in the commit