Bump minimum version of Slevomat coding standard

Author: colinodell

composer.json

@@ -33,7 +33,7 @@
     "require": {
         "php": "^7.1",
         "dealerdirect/phpcodesniffer-composer-installer": "^0.5.0",
-        "slevomat/coding-standard": "^6.2.0",
+        "slevomat/coding-standard": "~6.3.3",
         "squizlabs/php_codesniffer": "^3.4.0"
     },
     "require-dev": {