Avoid memory limits when running composer install

Author: Bruno Vitorino

.travis.yml

@@ -7,7 +7,7 @@ php:
 
 before_script:
   - travis_retry composer self-update
-  - travis_retry composer install --no-interaction --prefer-source
+  - COMPOSER_MEMORY_LIMIT=-1 travis_retry composer install --no-interaction --prefer-source
 
 script:
   - ./vendor/bin/simple-phpunit --coverage-text