Correct 7 ways to decompose fat activerecord models in README.md

[Ashish91]

This PR corrects the url for the blog 7 ways to decompose fat active record models. The url has been changed from http://blog.codeclimate.com/blog/2012/10/17/7-ways-to-decompose-fat-activerecord-models to https://codeclimate.com/blog/7-ways-to-decompose-fat-activerecord-models.