diff --git a/.travis.yml b/.travis.yml
index bf404e5..54ca0e0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,26 +1,29 @@
 language: php
 
-sudo: required
+sudo: false
 
 dist: trusty
 
 php:
   - 5.6
+    env: 'COMPOSER_FLAGS="--prefer-stable --prefer-lowest"'
   - 7.0
+    env: 'COMPOSER_FLAGS="--prefer-source"'
   - 7.1
+    env: 'COMPOSER_FLAGS="--prefer-source"'
 
 global:
   - REPORT_EXIT_STATUS=1
 
 before_script:
   - composer self-update
-  - composer install --prefer-source --no-interaction --dev
+  - composer install ${COMPOSER_FLAGS} --no-interaction --dev
 
 script:
   - vendor/bin/phpunit --coverage-clover build/logs/clover.xml
 
 after_script:
-  - vendor/bin/coveralls -v
+  - vendor/bin/coveralls -v --exclude-no-stmt
 
 matrix:
   fast_finish: true