Add Swift version to podspec

.swift-version

@@ -1 +0,0 @@
-4.2

ReachabilitySwift.podspec

@@ -22,4 +22,5 @@ Pod::Spec.new do |s|
   s.ios.framework    = 'CoreTelephony'
 
   s.requires_arc = true
+  s.swift_version = '5.0'
 end