Revert "Depend on stable versions (in preparation for PHPUnit 4.5 release)"

This reverts commit c6de7c0.

Author: sebastianbergmann

composer.json

@@ -20,6 +20,7 @@
         "issues": "https://github.com/sebastianbergmann/phpunit/issues",
         "irc": "irc://irc.freenode.net/phpunit"
     },
+    "minimum-stability": "dev",
     "require": {
         "php": ">=5.3.3",
         "phpunit/php-file-iterator": "~1.3",