[travis-ci] Ensure composer install is always done

Retry the operation if a network split occur and ignore system requirements for avoid errors if a required extension is disabled

Author: Maks3w

.travis.yml

@@ -30,7 +30,7 @@ before_install:
   - composer self-update
 
 install:
-  - composer install
+  - travis_retry composer install --no-interaction --ignore-platform-reqs
 
 script:
   - if [[ $EXECUTE_COVERAGE == 'true' ]]; then ./vendor/bin/phpunit --coverage-clover clover.xml ; fi