Upgrade to laravel 6.* (andywer#67)

* Upgrade to laravel 6.*

* Remove PHP 7.1 build from Travis as Laravel 6.0 requires a 7.2 minimum

* Change mockery calls

Author: Matthijsvdorp

.travis.yml

@@ -2,7 +2,6 @@ language: php
 sudo: false
 
 php:
-  - 7.1
   - 7.2
   - 7.3
 

composer.json

@@ -10,13 +10,13 @@
         }
     ],
     "require": {
-        "php": ">=5.4.0",
-        "illuminate/support": "^5.8"
+        "php": ">=7.1.0",
+        "illuminate/support": "6.*"
     },
     "require-dev": {
         "mockery/mockery": "~1.0",
-        "orchestra/testbench": "3.8.*",
-        "phpunit/phpunit": "^7.5"
+        "orchestra/testbench": "4.*",
+        "phpunit/phpunit": "^8.0"
     },
     "autoload": {
         "psr-4": {