Update metadata

Author: nnsnodnb

Package.resolved

@@ -9,7 +9,7 @@
 ```ruby
 pod 'swift-http-structured-headers',
     :git => 'https://github.com/nnsnodnb/apple-swift-http-structured-headers-podspec.git',
-    :tag => '1.5.0'
+    :tag => '1.6.0'
 ```
 
 Following to Swift Package Manager's usage.

README.md

@@ -1,6 +1,6 @@
 Pod::Spec.new do |spec|
   spec.name                  = 'swift-http-structured-headers'
-  spec.version               = '1.5.0'
+  spec.version               = '1.6.0'
   spec.license               = { :type => 'Apache License, Version 2.0', :file => 'LICENSE' }
   spec.homepage              = 'https://github.com/apple/swift-http-structured-headers'
   spec.author                = 'Apple Inc. and the SwiftNIO project'