Merge pull request #4399 from Rubenfer/master

Increase iOS version to 9 in Package.swift

Author: liuxuan30

Package.swift

@@ -5,7 +5,7 @@ import PackageDescription
 let package = Package(
     name: "Charts",
     platforms: [
-          .iOS(.v8),
+          .iOS(.v9),
           .tvOS(.v9),
           .macOS(.v10_11),
     ],