Installation failed, your reqs couldn't be resolved

[brouiller]

When I ran the command, "composer require jasongrimes/silex-simpleuser", I received the error below.

php composer.phar require jasongrimes/silex-simpleuser
Using version ^2.0 for jasongrimes/silex-simpleuser
./composer.json has been updated
Loading composer repositories with package information
Updating dependencies (including require-dev)
Your requirements could not be resolved to an installable set of packages.

Problem 1

• jasongrimes/silex-simpleuser 2.0.1 requires doctrine/dbal ~2.4 -> no matching package found.
• jasongrimes/silex-simpleuser 2.0 requires doctrine/dbal ~2.4 -> no matching package found.
• Installation request for jasongrimes/silex-simpleuser ^2.0 -> satisfiable by jasongrimes/silex-simpleuser[2.0, 2.0.1].

Potential causes:

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

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

Installation failed, reverting ./composer.json to its original content.