Add Laravel 7 support

Author: ssx

composer.json

@@ -27,12 +27,12 @@
     },
     "minimum-stability": "stable",
     "require": {
-        "illuminate/contracts": "^5.5|^6.0",
-        "illuminate/support": "^5.5|^6.0"
+        "illuminate/contracts": "^5.5|^6.0|^7.0",
+        "illuminate/support": "^5.5|^6.0|^7.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.0|^8.0",
-        "orchestra/testbench": "^3.5|^4.0"
+        "phpunit/phpunit": "^7.0|^8.0|^9.0",
+        "orchestra/testbench": "^3.5|^4.0|^5.0"
     },
     "suggest": {}
 }