Fix Travis config

.travis.yml

@@ -1,21 +1,25 @@
 language: php
+sudo: false
+
+php:
+  - 7.1
+  - 7.0
 
 notifications:
   email:
     on_success: never
     on_failure: change
 
-php:
-  - 7.1
-  - 7.0
-
-before_script:
+before_install:
   - composer self-update
-  - composer install --no-interaction --dev
+
+install:
+  - composer validate
+  - composer install -o --prefer-dist --no-interaction
 
 script:
  - mkdir -p build/logs
  - php vendor/bin/phpunit --coverage-clover build/logs/clover.xml
 
 after_script:
- - php vendor/bin/coveralls -v
+ - php vendor/bin/coveralls -v