minor #32 Allow Symfony 4 (dunglas)

This PR was merged into the 1.0-dev branch.

Discussion
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Allow Symfony 4

Commits
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97635f1 Allow Symfony 4

composer.json

@@ -18,10 +18,10 @@
     "require": {
         "php": ">=5.3.3",
         "psr/http-message": "~1.0",
-        "symfony/http-foundation": "~2.3|~3.0"
+        "symfony/http-foundation": "~2.3|~3.0|~4.0"
     },
     "require-dev": {
-        "symfony/phpunit-bridge": "~3.2"
+        "symfony/phpunit-bridge": "~3.2|4.0"
     },
     "suggest": {
         "psr/http-message-implementation": "To use the HttpFoundation factory",