Fix composer --dev install on PHP 5.3.

Though the version of PHPUnit specifiied only requires 5.3, the code-coverage dependency master branch (1.3.x-dev) required 5.4. 1.2.x-dev is the PHPUnit 3.7 branch.

Signed-off-by: Max Fierke <max@maxfierke.com>
Merge pull request #139 from maxfierke/master

Fix `composer --dev install` on PHP 5.3