build: Fix the PHP-CS-Fixer dependency (#111)

Remove the PHAR accidentally committed in
#103 and introduce the
PHP-CS-Fixer shim instead.

Author: theofidry

composer.json

@@ -47,7 +47,8 @@
         "phpspec/prophecy": "^1.14.0",
         "phpspec/prophecy-phpunit": "^2.0",
         "monolog/monolog": "^3.5",
-        "symfony/runtime": "*"
+        "symfony/runtime": "*",
+        "php-cs-fixer/shim": "^3.94"
     },
 
     "extra": {