Add support for PHP 8.1.

Author: ivopetkov

composer.json

@@ -15,11 +15,10 @@
         }
     ],
     "require": {
-        "php": "7.0.*|7.1.*|7.2.*|7.3.*|7.4.*|8.0.*",
+        "php": "7.0.*|7.1.*|7.2.*|7.3.*|7.4.*|8.0.*|8.1.*",
         "ivopetkov/html5-dom-document-php": "2.*"
     },
     "require-dev": {
-        "phpunit/phpunit": "6.*|7.*|8.*|9.*",
         "ivopetkov/docs-generator": "0.1.*"
     },
     "autoload": {

src/HTMLServerComponent.php

@@ -172,7 +172,7 @@ public function __toString(): string
     {
         $html = '<' . $this->tagName;
         foreach ($this->attributes as $name => $value) {
-            $html .= ' ' . $name . '="' . htmlspecialchars($value) . '"';
+            $html .= ' ' . $name . '="' . htmlspecialchars((string)$value) . '"';
         }
         return $html . '>' . $this->innerHTML . '</' . $this->tagName . '>';
     }