Translate "ChangeLog" for Japanese.
Merge pull request #40 from fluent/translate/ja/changelog

Translate "ChangeLog" for Japanese.
Adjustment of wording.
Fix typo.
Translate "Troubleshooting Fluentd" for Japanese.
Merge pull request #41 from fluent/translate/ja/trouble-shooting

Translate "Troubleshooting Fluentd" for Japanese.