Upgrade testbench

Author: barryvdh

composer.json

@@ -39,7 +39,7 @@
     },
     "require-dev": {
         "squizlabs/php_codesniffer": "^2.3",
-        "orchestra/testbench": "^3|^4|^5|^6|^7"
+        "orchestra/testbench": "^7|^8"
     },
     "scripts": {
         "test": "phpunit",