Fix Swift 4 implementation

This adds swift version property to the podspec, as well as using the appropriate notification names. It fixes some discrepancies that were preventing this from building in Xcode 10.1.

RSBarcodes_Swift.podspec

@@ -1,6 +1,6 @@
 Pod::Spec.new do |s|
  s.name = "RSBarcodes_Swift"
- s.version = "4.2.0"
+ s.version = "4.2.1"
  s.summary = "1D and 2D barcodes reader and generators for iOS 8 with delightful controls. Now Swift. "
  s.homepage = "https://github.com/yeahdongcn/RSBarcodes_Swift"
  s.license = { :type => 'MIT', :file => 'LICENSE.md' }
@@ -10,4 +10,5 @@ Pod::Spec.new do |s|
  s.source_files = 'Source/*.{swift,h,m}'
  s.frameworks = ['CoreImage', 'AVFoundation', 'QuartzCore']
  s.requires_arc = true
+ s.swift_version = "4.0"
 end

Source/RSCodeReaderViewController.swift

@@ -376,9 +376,9 @@ open class RSCodeReaderViewController: UIViewController, AVCaptureMetadataOutput
 
  override open func viewDidDisappear(_ animated: Bool) {
  super.viewDidDisappear(animated)
- 
- NotificationCenter.default.removeObserver(self, name: UIApplication.willEnterForegroundNotification, object: nil)
- NotificationCenter.default.removeObserver(self, name: UIApplication.didEnterBackgroundNotification, object: nil)
+
+ NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationWillEnterForeground, object: nil)
+ NotificationCenter.default.removeObserver(self, name: NSNotification.Name.UIApplicationDidEnterBackground, object: nil)
  if !Platform.isSimulator {
  self.session.stopRunning()
  }