Update dependencies

Author: Justin Hayes

composer.json

@@ -23,7 +23,7 @@
         }
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.4",
+        "phpunit/phpunit": "^6.0|^7.0",
         "orchestra/testbench": "^3.0",
         "mockery/mockery": "^1.2"
     },