Masatora Atarashi

@okmr-d Hello. Thank you for the wonderful pods. I would like this change merged. Works perfectly with my Xcode 11 & Swift 5. Thank you.

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【付録A Go言語のJSONのパース】A2.1 『出力時に出力を加工する』に出てくるサンプルコードを追加しました。 (サンプルコード無しだと理解し辛かったので)