[stzn/the-swift-programming-language-jp] Pull request closed: #506 CやObjective-Cとの比較している箇所を削除

[stzn/the-swift-programming-language-jp] Issue closed: #503 Swiftの紹介について記述の更新

[stzn/the-swift-programming-language-jp] Issue closed: #505 クロージャの説明変更

[stzn/the-swift-programming-language-jp] Issue closed: #502 taskGroupをgroupに変える

[stzn/the-swift-programming-language-jp] New comment on issue #502: taskGroupをgroupに変える