Add symfony/polyfill-php70 explicitly

Author: terox

composer.json

@@ -14,6 +14,7 @@
         "php": ">=5.5.3",
         "doctrine/common": "~2.2",
         "doctrine/orm": "~2.2",
+        "symfony/polyfill-php70": "^1.3",
         "symfony/security": "^2.8|^3.0",
         "symfony/options-resolver": "^2.8|^3.0",
         "ircmaxell/random-lib": "~1.0"