bug #9 Allow Symfony 4.0 (piotrantosik)

This PR was merged into the master branch.

Discussion
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Allow Symfony 4.0

It required by https://github.com/symfony/debug-pack/blob/master/composer.json#L9

Commits
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4a1ee25 Allow Symfony 4.0

composer.json

@@ -17,7 +17,7 @@
     "require": {
         "php"             : ">=5.3.0",
         "monolog/monolog" : "~1.6",
-        "symfony/yaml"    : "~2.3|~3.0"
+        "symfony/yaml"    : "~2.3|~3.0|~4.0"
     },
     "autoload": {
         "psr-4": { "EasyCorp\\EasyLog\\": "src" }