Remove dev switch from travis command

Author: Matt Humphrey

.travis.yml

@@ -9,7 +9,7 @@ php:
 
 before_script:
   - travis_retry composer self-update
-  - travis_retry composer install --no-interaction --prefer-source --dev
+  - travis_retry composer install --no-interaction --prefer-source
 
 script:
   - vendor/bin/phpunit --verbose --coverage-text