Update filename/links: coc -> code_of_conduct

Author: yasulab

CODE_OF_CONDUCT.md

@@ -4,9 +4,9 @@ CoderDojo Japan team is committed to fostering a welcoming community.
 
 **Our Code of Conduct can be found here**:
 
-https://coderdojo.jp/docs/coc
+https://coderdojo.jp/docs/code_of_conduct
 
 For a history of updates, see the page history here:
 
-https://github.com/coderdojo-japan/coderdojo.jp/commits/master/db/docs/coc.md
+https://github.com/coderdojo-japan/coderdojo.jp/commits/master/db/docs/code_of_conduct.md