Update minimum required Swift version in a few places (#190)

README.md

@@ -9,7 +9,7 @@ A sweet and swifty [YAML](http://yaml.org/) parser built on
 
 ## Installation
 
-Building Yams requires Xcode 10.x or a Swift 4.x/5.x toolchain with the
+Building Yams requires Xcode 10.x or a Swift 4.1+/5.x toolchain with the
 Swift Package Manager.
 
 ### Swift Package Manager

Sources/Yams/Constructor.swift

@@ -456,8 +456,7 @@ extension Set {
         // TODO: YAML supports Hashable elements other than str.
         return Set<AnyHashable>(mapping.map({ String.construct(from: $0.key)! as AnyHashable }))
         // Explicitly declaring the generic parameter as `<AnyHashable>` above is required,
-        // because this is inside extension of `Set` and Swift 4.0.x can't infer the type without
-        // that.
+        // because this is inside extension of `Set` and Swift can't infer the type without that.
     }
 }
 

Yams.podspec

@@ -8,7 +8,7 @@ Pod::Spec.new do |s|
   s.authors                   = { 'JP Simard' => 'jp@jpsim.com',
                                   'Norio Nomura' => 'norio.nomura@gmail.com' }
   s.source_files              = 'Sources/**/*.{h,c,swift}'
-  s.swift_versions            = ['4.0', '4.1', '4.2', '5.0']
+  s.swift_versions            = ['4.1', '4.2', '5.0']
   s.pod_target_xcconfig       = { 'APPLICATION_EXTENSION_API_ONLY' => 'YES' }
   s.ios.deployment_target     = '8.0'
   s.osx.deployment_target     = '10.9'