Use --prefer-dist option instead

Author: lucasmichot

.travis.yml

@@ -21,9 +21,9 @@ matrix:
       env: setup=stable
 
 install:
-  - if [[ $setup = 'basic' ]]; then travis_retry composer install --no-interaction --prefer-source; fi
-  - if [[ $setup = 'stable' ]]; then travis_retry composer update --prefer-source --no-interaction --prefer-stable; fi
-  - if [[ $setup = 'lowest' ]]; then travis_retry composer update --prefer-source --no-interaction --prefer-lowest --prefer-stable; fi
+  - if [[ $setup = 'basic' ]]; then travis_retry composer install --no-interaction --prefer-dist; fi
+  - if [[ $setup = 'stable' ]]; then travis_retry composer update --prefer-dist --no-interaction --prefer-stable; fi
+  - if [[ $setup = 'lowest' ]]; then travis_retry composer update --prefer-dist --no-interaction --prefer-lowest --prefer-stable; fi
 
 script:
   - vendor/bin/phpunit