update japanese translation

i18n/ja.yaml

@@ -15,10 +15,10 @@ article:
   word_count:
     one: "{{ .Count }} 文字"
     other: "{{ .Count }} 文字"
-  part_of_series: "This article is part of a series."
-  part: "Part"
-  this_article: "This Article"
-  related_articles: "Related"
+  part_of_series: "この記事は連載の一部です"
+  part: "パート"
+  this_article: "この記事"
+  related_articles: "関連記事"
 
 author:
   byline_title: "著者"