Use named link reference for recently added link

Author: stomar

en/documentation/index.md

@@ -61,7 +61,7 @@ the [installation guide](installation/) for help on installing Ruby.
 
 ### Reference Documentation
 
-[Official API Documentation][40]
+[Official API Documentation][docs-rlo-en]
 : The official Ruby API documentation for different versions including
   the currently unreleased (trunk) version.
 
@@ -170,6 +170,6 @@ If you have questions about Ruby the
 [37]: http://www.sublimetext.com/
 [38]: http://ruby.learncodethehardway.org/
 [39]: http://kapeli.com/dash
-[40]: https://docs.ruby-lang.org/en/
+[docs-rlo-en]: https://docs.ruby-lang.org/en/
 [atom]: https://atom.io/
 [vscode]: https://code.visualstudio.com/

ko/documentation/index.md

@@ -69,7 +69,7 @@ lang: ko
 
 ### 참조
 
-[공식 API 문서][40]
+[공식 API 문서][docs-rlo-en]
 : 아직 릴리스되지 않은 트렁크를 포함한 여러 루비 버전의 공식 API 문서입니다.
 
 [루비 코어 레퍼런스][13] (영문)
@@ -172,7 +172,7 @@ lang: ko
 [37]: http://www.sublimetext.com/
 [38]: http://ruby.learncodethehardway.org/
 [39]: http://kapeli.com/dash
-[40]: https://docs.ruby-lang.org/en/
+[docs-rlo-en]: https://docs.ruby-lang.org/en/
 [atom]: https://atom.io/
 [vscode]: https://code.visualstudio.com/
 

zh_tw/documentation/index.md

@@ -49,7 +49,7 @@ lang: zh_tw
 
 ### 參考文件
 
-[Official API Documentation][40]
+[Official API Documentation][docs-rlo-en]
 : 各種版本的 Ruby 官方 API 文件，包含當前未釋出的版本（trunk）。
 
 [Ruby Core Reference][13]
@@ -143,7 +143,7 @@ lang: zh_tw
 [37]: http://www.sublimetext.com/
 [38]: http://ruby.learncodethehardway.org/
 [39]: http://kapeli.com/dash
-[40]: https://docs.ruby-lang.org/en/
+[docs-rlo-en]: https://docs.ruby-lang.org/en/
 [atom]: https://atom.io/
 [vscode]: https://code.visualstudio.com/