Add PHP 8 support, test and laravel version test (#125)

* Add PHP 8 support, test and laravel version test

* ci fix

Author: thecaliskan

.travis.yml

@@ -4,11 +4,12 @@ php:
   - 7.2
   - 7.3
   - 7.4
+  - 8.0
 
 env:
-  matrix:
-    - COMPOSER_FLAGS="--prefer-lowest"
-    - COMPOSER_FLAGS=""
+    matrix:
+        - COMPOSER_FLAGS="--prefer-lowest"
+        - COMPOSER_FLAGS=""
 
 before_script:
   - travis_retry composer self-update

composer.json

@@ -25,7 +25,7 @@
         }
     ],
     "require": {
-        "php": "^7.2.0",
+        "php": "^7.2.0|^8.0",
         "berkayk/onesignal-laravel": "^1.0.0",
         "illuminate/notifications": "5.*|^6.0|^7.0|^8.0",
         "illuminate/support": "5.*|^6.0|^7.0|^8.0"