Supports for RxSwift 6.0

Merge pull request #19 from bigMOTOR/feature/Upgrade-to-RxSwift-6.0

RxSwift 6

Support the swift package manager

1.3.0

Support the swift package manager

Add SKReceiptRefreshRequest support

1.2.1

Update version for 1.2.1

Support Swift 4.0

• Swift 4.0 support
• Finishing a transaction is now the responsibility of who implements the observables

Support for iOS9

1.0.1

Modify podspec

1.0.0

Merge remote-tracking branch 'origin/master'