Update composer.json

Author: ivailop

composer.json

@@ -3,7 +3,7 @@
         "phpunit/phpunit": "4.8.*",
         "phpunit/dbunit": ">=1.2",
         "phpunit/phpcov": "*",
-        "squizlabs/php_codesniffer": "2.*",
+        "squizlabs/php_codesniffer": "3.*",
         "phpmd/phpmd" : "@stable"
     }
-  }
+  }