Fix path typo.

platforms/php/build.php

@@ -61,7 +61,7 @@ class Component_Builder {
   }
 
   function build(): void {
-    $root_path = __DIR__ . '/' . $this->module_path . '../..';
+    $root_path = __DIR__ . '/' . $this->module_path . '/../..';
     $file_name = $this->get_handlebars_template( "$root_path/src/$this->component_name.template.hbs" );
 
     $output_folder = $root_path . '/exports/wordpress/templates';