Use String#encode instead NKF
Merge pull request #190 from ayumin/kill-ruby18

Use String#encode instead NKF
.gitkeep might not be a good name for other SCM users
Fixed typo and add test
Merge pull request #192 from ayumin/typo/const_ste

Fixed typo and add test
Fix crawler to save modified items
Merge pull request #193 from iwamot/fix_crawler

Fix crawler to save modified items
Merge pull request #191 from ayumin/kill-gitkeep

.gitkkep might not be a good name for other SCM users