Fixes #5 and #7

* Fixed create_uuid() with your comment.
* Fixed test_create_category with mock.
* Added .tracis.yml, so would you set up travis from as following?
 1. Create account with github account from https://travis-ci.org/
 2. Settings of projects -> Webhooks & Services -> Configure Services -> Select "travis",
   then input your github account in "User", and "token" retrieve from travis account profile in "Token",
   check "Active", and pressing "Update settings".