Specify Swift Version

Author: Ben Deckys

Diff for: UICollectionViewLeftAlignedLayout.podspec

@@ -18,4 +18,5 @@ Pod::Spec.new do |s|
   s.source       = { :git => "https://github.com/mokagio/UICollectionViewLeftAlignedLayout.git", :tag => version }
   s.source_files  = "UICollectionViewAlignedLayout"
   s.requires_arc = true
+  s.pod_target_xcconfig = { 'SWIFT_VERSION' => '4' }	
 end