Fix return type

Author: AydinHassan

src/Util/StringUtil.php

@@ -44,7 +44,7 @@ public static function stripAnsiEscapeSequence(string $str) : string
         return (string) preg_replace('/\x1b[^m]*m/', '', $str);
     }
 
-    public static function length(string $str, bool $ignoreAnsiEscapeSequence = true) : string
+    public static function length(string $str, bool $ignoreAnsiEscapeSequence = true) : int
     {
         return mb_strlen($ignoreAnsiEscapeSequence ? self::stripAnsiEscapeSequence($str) : $str);
     }