Update dependencies

Author: petericebear

.travis.yml

@@ -1,9 +1,10 @@
 language: php
 
 php:
-  - 5.6
   - 7.0
   - 7.1
+  - 7.2
+  - 7.3
 
 env:
   matrix:

composer.json

@@ -1,21 +1,20 @@
 {
     "name": "laravel-notification-channels/messagebird",
-    "description": "MessageBird notification channel for Laravel 5.3",
+    "description": "MessageBird notification channel for Laravel 5.x",
     "homepage": "https://github.com/laravel-notification-channels/messagebird",
     "license": "MIT",
     "authors": [
         {
             "name": "Peter Steenbergen",
             "email": "[email protected]",
-            "homepage": "http://3ws.nl",
+            "homepage": "https://3ws.nl",
             "role": "Developer"
         }
     ],
     "require": {
-        "php": ">=5.6.4",
-        "illuminate/notifications": "^5.3",
-        "illuminate/support": "^5.1|^5.2|^5.3",
-        "illuminate/queue": "^5.3",
+        "illuminate/notifications": "5.5.*|5.6.*|5.7.*|5.8.*",
+        "illuminate/support": "5.5.*|5.6.*|5.7.*|5.8.*",
+        "illuminate/queue": "5.5.*|5.6.*|5.7.*|5.8.*",
         "guzzlehttp/guzzle": "^6.2"
     },
     "require-dev": {