fix the document and add gem 'thor' to Gemfile for PaaS

- Fix the doc/INSTALL-paas.md to use bin/tdiary command
- Add gem 'thor' to Gemfile to deploy to heroku
Merge pull request #428 from Nyoho/fix-doc-and-gemfile-for-paas

fix the document and add gem 'thor' to Gemfile for PaaS