work with build matrix

.travis.yml

@@ -7,7 +7,17 @@ services:
   - rabbitmq
   - redis-server
 
+matrix:
+  include:
+    - php: 7.0
+      env: dependencies=lowest
+    - php: 7.0
+      env: dependencies=highest
+
 before_script:
-  - composer --prefer-source --dev install
+  - composer self-update -q
+  - if [ -z "$dependencies" ]; then composer install; fi;
+  - if [ "$dependencies" = "lowest" ]; then composer update --prefer-lowest -n; fi;
+  - if [ "$dependencies" = "highest" ]; then composer update -n; fi;
 
 script: phpunit --coverage-text --verbose