cakephp/cakephp — pull request #4755 by ADmad (2014-09-28 20:02:49+00:00)
Title: Change default replacement for Inflector::slug().

Use dash instead of underscore.

> We recommend that you use hyphens (-) instead of underscores (_) in your URLs.

[Source](https://support.google.com/webmasters/answer/76329?hl=en).

Majority of the sites use dash for slugs.