Run tests against various illuminate versions

Author: Jaspaul

.travis.yml

@@ -1,10 +1,28 @@
 language: php
 
-php:
-  - 7.0
-  - 7.1
+matrix:
+  include:
+    - php: 7.0
+      env: ILLUMINATE_VERSION=5.4.*
+    - php: 7.0
+      env: ILLUMINATE_VERSION=5.5.*
+    - php: 7.1
+      env: ILLUMINATE_VERSION=5.4.*
+    - php: 7.1
+      env: ILLUMINATE_VERSION=5.5.*
+    - php: 7.2
+      env: ILLUMINATE_VERSION=5.4.*
+    - php: 7.2
+      env: ILLUMINATE_VERSION=5.5.*
 
-before_script: composer install
+before_install:
+  - composer require "illuminate/cache:${ILLUMINATE_VERSION}" --no-update
+  - composer require "illuminate/config:${ILLUMINATE_VERSION}" --no-update
+  - composer require "illuminate/console:${ILLUMINATE_VERSION}" --no-update
+  - composer require "illuminate/database:${ILLUMINATE_VERSION}" --no-update
+  - composer require "illuminate/support:${ILLUMINATE_VERSION}" --no-update
+
+before_script: composer update --prefer-source --no-interaction --dev
 
 script:
   - vendor/bin/phpunit