Support Xcode 12

[DenTelezhkin]

Xcode 12 bumps minimum iOS deployment target to iOS 9. Several changes have been made to go along with this:

1. Changed minimum iOS target in Package.swift
2. iOS deployment target in CocoaPods bumped to iOS 9
3. iOS deployment target in Xcode project bumped to iOS 9.
4. Used Xcode 12 recommended settings.

[DivineDominion]

Thanks for the update, and thanks a lot for contributing to SwiftCSV! We've invited you to join the SwiftCSV GitHub organization – no pressure to accept! If you'd like more information on what that means, check out our contributor guidelines.

[DenTelezhkin]

Thank you! 🚀