Updates param collection to correctly set key/value pairs when conver…

…ting to string (#60)

lib/Registries/Param_Collection.php

@@ -72,7 +72,7 @@ public function __toString(): string {
 	public function to_string(): string {
 		return (string) ( new Array_Processor( $this->to_array() ) )
 			->values()
-			->each( fn ( Param $value ) => $value->to_string() )
+			->each( fn ( Param $value ) => $value->get_id() . '=' . $value->to_string() )
 			->set_separator( '&' );
 	}