update plugins.md based e57cd00. fix #175
modify based on comments
_posts以下のファイルをIssue
update variables.md
fix typo in our CONTRIBUTING.md
rake-togglate now succeeds
update upgrading.md
update troubleshooting.md
Merge pull request #239 from satoso/contrib_typo

fix typo in our CONTRIBUTING.md
Merge pull request #240 from satoso/iss183

update upgrading.md
Merge pull request #241 from satoso/iss182

update troubleshooting.md
Merge pull request #209 from melborne/update-plugins.md

update plugins.md based e57cd00. fix #175
Merge pull request #238 from satoso/iss185

update variables.md
Merge pull request #236 from jekyllrb-ja/create_posts_diff

_posts以下のファイルをIssue化