Specift swift version 4.2 in podspec

Author: tsolomko

BitByteData.podspec

@@ -20,7 +20,7 @@ Pod::Spec.new do |s|
   s.tvos.deployment_target = "9.0"
   s.watchos.deployment_target = "2.0"
 
-  s.swift_version = "4.1"
+  s.swift_version = "4.2"
 
   s.source_files = "Sources/*.swift"