Update composer.json

Author: barryvdh

composer.json

@@ -17,12 +17,12 @@
         }
     ],
     "require": {
-        "php": ">=5.3.0",
+        "php": ">=5.6",
         "psr/log": "^1.0",
-        "symfony/var-dumper": "^2.6|^3.0|^4.0"
+        "symfony/var-dumper": "^2.6|^3|^4"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.0|^5.0"
+        "phpunit/phpunit": "^5"
     },
     "autoload": {
         "psr-4": {