Merge pull request #498 from drbyte/symfony4-compat

Add compatibility with symfony/process v4

Author: adamwathan

composer.json

@@ -27,7 +27,7 @@
         "php": ">=5.6",
         "illuminate/container": "~5.1",
         "mnapoli/silly": "~1.0",
-        "symfony/process": "~2.7|~3.0",
+        "symfony/process": "~2.7|~3.0|~4.0",
         "nategood/httpful": "~0.2",
         "tightenco/collect": "^5.3"
     },