Allow custom output path for static and external_static instead o…

…f only `static` (#884)

src/Writing/HtmlWriter.php

@@ -30,7 +30,7 @@ public function __construct(DocumentationConfig $config = null)
         // If they're using the default static path,
         // then use '../docs/{asset}', so assets can work via Laravel app or via index.html
         $this->assetPathPrefix = '../docs/';
-        if ($this->config->get('type') == 'static'
+        if (in_array($this->config->get('type'), ['static', 'external_static'])
             && rtrim($this->config->get('static.output_path', ''), '/') != 'public/docs'
         ) {
             $this->assetPathPrefix = './';