Add Japanese translation link

Author: mitsuruog

README.md

@@ -2174,5 +2174,6 @@ This is also available in other languages:
  - [BoryaMogila/clean-code-javascript-ru/](https://github.com/BoryaMogila/clean-code-javascript-ru/)
  - [maksugr/clean-code-javascript](https://github.com/maksugr/clean-code-javascript)
  - ![vi](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Vietnam.png) **Vietnamese**: [hienvd/clean-code-javascript/](https://github.com/hienvd/clean-code-javascript/)
+ - ![ja](https://raw.githubusercontent.com/gosquared/flags/master/flags/flags/shiny/24/Japan.png) **Japanese**: [mitsuruog/clean-code-javascript/](https://github.com/mitsuruog/clean-code-javascript/)
 
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