Revert "removed 3.0 constraints from 2.7 composer files"

This reverts commit 5503804cf91f4ede81b94b34609653c013139038.

Author: fabpot

composer.json

@@ -19,10 +19,10 @@
         "php": ">=5.3.9"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "~2.7",
-        "symfony/yaml": "~2.1",
-        "symfony/config": "~2.2",
-        "symfony/expression-language": "~2.6"
+        "symfony/phpunit-bridge": "~2.7|~3.0.0",
+        "symfony/yaml": "~2.1|~3.0.0",
+        "symfony/config": "~2.2|~3.0.0",
+        "symfony/expression-language": "~2.6|~3.0.0"
     },
     "conflict": {
         "symfony/expression-language": "<2.6"