allow version 5 of the Symfony Process component (#47)

Author: xabbuh

composer.json

@@ -13,7 +13,7 @@
   ],
   "require": {
     "php": "^7.1.0",
-    "symfony/process": "^4.0"
+    "symfony/process": "^4.0|^5.0"
   },
   "require-dev": {
     "phpunit\/phpunit": "^7.0",