[5.4] fixed BuildsQueries when docblock (#19396)

* fixed BuildsQueries when docblock

* Update BuildsQueries.php

Author: fragkp

src/Illuminate/Database/Concerns/BuildsQueries.php

@@ -79,8 +79,8 @@ public function first($columns = ['*'])
      * Apply the callback's query changes if the given "value" is true.
      *
      * @param  mixed  $value
-     * @param  \Closure  $callback
-     * @param  \Closure  $default
+     * @param  callable  $callback
+     * @param  callable  $default
      * @return mixed
      */
     public function when($value, $callback, $default = null)