Removed composer self-update

Author: slavvka

.travis.yml

@@ -9,7 +9,6 @@ matrix:
   fast_finish: true
 
 before_install:
-  - travis_retry composer self-update
   - composer install --prefer-source --no-interaction --dev
 
 script: php vendor/phpunit/phpunit/phpunit --configuration tests/Unit/phpunit.xml.dist