Fix typos, modernize os(OSX) → os(macOS), and clean up Notification.Name bridging in XCPlayground#80

crleonard wants to merge 4 commits into

apple:mainapple/swift-xcode-playground-support:mainfrom

crleonard:fix/typos-and-os-macOS-modernizationcrleonard/swift-xcode-playground-support:fix/typos-and-os-macOS-modernizationCopy head branch name to clipboard