Add Laravel 8 support (#22)

* Add Laravel 6 support
* Add Laravel 7 support
* Add Laravel 8 support

Co-authored-by: Wilbur Zhao <wilbur.zhao@vertogroup.com.au>

Author: WilburJZHAO

composer.json

@@ -41,8 +41,8 @@
     },
     "require": {
         "php": "^5.6|^7.0",
-        "illuminate/database": "~5.2|~5.3|~5.4|~5.5|~5.6|~5.7",
-        "illuminate/support": "~5.2|~5.3|~5.4|~5.5|~5.6|~5.7"
+        "illuminate/database": "^5.2|^6.0|^7.0|^8.0",
+        "illuminate/support": "^5.2|^6.0|^7.0|^8.0"
     },
     "require-dev": {
         "friendsofphp/php-cs-fixer": "^2.10",