travis: fix phpcs bin path

Author: ek9

.travis.yml

@@ -17,6 +17,6 @@ before_script:
   - if [[ $deps = low ]]; then composer update --prefer-lowest --prefer-stable; else composer update; fi
 
 script:
-  - bin\phpcs
+  - ./bin/phpcs
   - ./bin/phpunit -vvv