composer update instead of install

Author: fbourigault

.travis.yml

@@ -16,7 +16,7 @@ matrix:
 
 before_script:
   - travis_retry composer self-update
-  - travis_retry composer install --no-interaction ${COMPOSER_FLAGS}
+  - travis_retry composer update --no-interaction ${COMPOSER_FLAGS}
   - if [ "$STATIC_ANALYSIS" != "" ]; then curl -L https://github.com/phpstan/phpstan/releases/download/0.8/phpstan.phar -o phpstan.phar; fi;
 
 script: