Fix: Prefer packages installed from dist

Author: localheinz

.travis.yml

@@ -18,7 +18,7 @@ before_install:
   - composer selfupdate
 
 install:
-  - travis_retry composer install --no-interaction --prefer-source
+  - composer install --no-interaction --prefer-dist
   - if [[ "$CHECK_LINKS" == "true" ]]; then sudo apt-get -y install pypy python-sphinx graphviz; fi
 
 script: