add laravel 5.6, php 7.2 support to travis config

Author: michaeldyrynda

.travis.yml

@@ -16,6 +16,14 @@ matrix:
       env: ILLUMINATE_VERSION=5.4.*
     - php: 7.1
       env: ILLUMINATE_VERSION=5.5.*
+    - php: 7.1
+      env: ILLUMINATE_VERSION=5.6.*
+    - php: 7.2
+      env: ILLUMINATE_VERSION=5.4.*
+    - php: 7.2
+      env: ILLUMINATE_VERSION=5.5.*
+    - php: 7.2
+      env: ILLUMINATE_VERSION=5.6.*
 
 before_install:
   - composer require "illuminate/database:${ILLUMINATE_VERSION}" --no-update -v