upgrade PHPStan's level

Author: itosho

.travis.yml

@@ -40,7 +40,7 @@ script:
   - if [[ $DEFAULT = 1 && $TRAVIS_PHP_VERSION = 7.1 ]]; then vendor/bin/phpunit --coverage-clover=clover.xml; fi
 
   - if [[ $PHPCS = 1 ]]; then vendor/bin/phpcs -n -p --extensions=php --standard=vendor/cakephp/cakephp-codesniffer/CakePHP ./src ./tests; fi
-  - if [[ $PHPSTAN = 1 ]]; then vendor/bin/phpstan analyse -c phpstan.neon -l 5 src; fi
+  - if [[ $PHPSTAN = 1 ]]; then vendor/bin/phpstan analyse -c phpstan.neon -l 7 src; fi
 
 after_success:
   - if [[ $DEFAULT = 1 && $TRAVIS_PHP_VERSION = 7.1 ]]; then bash <(curl -s https://codecov.io/bash); fi