Install composer dependencies on hhvm / nightly anyway

Allows the installation of php-cs-fixer even though it conflicts with
hhvm / nightly. It's not actually used under these platforms, but is
listed in require-dev.

Author: erayd

.travis.yml

@@ -26,8 +26,8 @@ before_install:
   - composer selfupdate
 
 install:
-  - travis_retry composer install --no-interaction --prefer-dist
+  - if [[ "$TRAVIS_PHP_VERSION" != "hhvm" && "$TRAVIS_PHP_VERSION" != "nightly" ]]; then travis_retry composer install --no-interaction --prefer-dist; else travis_retry composer install --no-interaction --prefer-dist --ignore-platform-reqs; fi
 
 script:
   - if [[ "$WITH_COVERAGE" == "true" ]]; then ./vendor/bin/phpunit --coverage-text; else composer test; fi
-  - if [[ "$WITH_PHPCSFIXER" == "true" ]]; then composer require friendsofphp/php-cs-fixer:^2.1 && mkdir -p $HOME/.phpcsfixer && vendor/bin/php-cs-fixer fix --cache-file "$HOME/.phpcsfixer/.php_cs.cache" --dry-run --diff --verbose; fi
+  - if [[ "$WITH_PHPCSFIXER" == "true" ]]; then mkdir -p $HOME/.phpcsfixer && vendor/bin/php-cs-fixer fix --cache-file "$HOME/.phpcsfixer/.php_cs.cache" --dry-run --diff --verbose; fi