language: php
php:
    - 7.0
    - 7.1
install:
    - composer self-update && composer --version
    - composer install --dev
script:
    - vendor/bin/phpunit --verbose --coverage-clover=coverage.clover
    - vendor/bin/phpcs --standard=PSR2 --extensions=php src tests

language: php
php:
    - 7.0
    - 7.1
install:
    - composer self-update && composer --version
    - composer install
script:
    - vendor/bin/phpunit --verbose --coverage-clover=coverage.clover
    - vendor/bin/phpcs --standard=PSR2 --extensions=php src tests

Remove dev flag on composer install
Remove dev flag on composer install

It's deprecated and the default behavior is to install dev dependencies now.