Merge pull request #177 from coffe4u/upgrade-phpunit-to-version-8

Upgrade phpunit to version 8

Author: hannesvdvreken

.gitignore

@@ -1,3 +1,4 @@
 /.php_cs.cache
+/.phpunit.result.cache
 /composer.lock
 /vendor

composer.json

@@ -20,10 +20,10 @@
         "twilio/sdk": "^6.0"
     },
     "require-dev": {
+        "friendsofphp/php-cs-fixer": "^2.16",
         "illuminate/console": "~4||~5",
         "illuminate/support": "~4||~5",
-        "friendsofphp/php-cs-fixer": "^2.16",
-        "phpunit/phpunit": "^8.0"
+        "phpunit/phpunit": "~8.0"
     },
     "autoload": {
         "psr-4": {