Fix: SpecifyArgSeparatorFixer type error in PHP 7.4+

[OndraM]

Fixes #72 .

@janbarasek Could you please try it on your codebase?

In require-dev of composer.json:

    "lmc/coding-standard": "dev-fix/type-error",

[janbarasek]

Thank you, it now generates this diff:

    ---------- begin diff ----------
--- Original
+++ New
@@ -32,7 +32,7 @@
             }
         }
 
-        return (string) $refererUri->withQuery(http_build_query($cleanQueryParts));
+        return (string) $refererUri->withQuery(http_build_query($cleanQueryParts, '', '&'));
     }
 
     public function invalidGridFilterSettings(): void

    ----------- end diff -----------