Update README.md

[nepster-web]

"creocoder/yii2-nested-set-behavior": "*":

Your requirements could not be resolved to an installable set of packages.

Problem 1

• The requested package creocoder/yii2-nested-set-behavior could not be foun d in any version, there may be a typo in the package name.

Potential causes:

• A typo in the package name
• The package is not available in a stable-enough version according to your min imum-stability setting see https://groups.google.com/d/topic/composer-dev/_g3ASeIFlrc/discussion f or more details.

Read http://getcomposer.org/doc/articles/troubleshooting.md for further common problems.

https://packagist.org/packages/creocoder/yii2-nested-set-behavior

[creocoder]

Fixed