Revert "removed 3.0 constraints from 2.7 composer files"

This reverts commit 5503804cf91f4ede81b94b34609653c013139038.

Author: fabpot

composer.json

@@ -19,7 +19,7 @@
         "php": ">=5.3.9"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "~2.7"
+        "symfony/phpunit-bridge": "~2.7|~3.0.0"
     },
     "autoload": {
         "psr-0": { "Symfony\\Component\\OptionsResolver\\": "" }