http_build_query(): Passing null to parameter #2 ($numeric_prefix) of…

… type string is deprecated (#34)

Pass an empty string (the default value) instead.

Fixes #33

S3.php

@@ -2012,7 +2012,7 @@ public static function __getSignatureV4($amzHeaders, $headers, $method, $uri, $p
 		// Convert null query string parameters to strings and sort
 		$parameters = array_map('strval', $parameters); 
 		uksort($parameters, array('self', '__sortMetaHeadersCmp'));
-		$queryString = http_build_query($parameters, null, '&', PHP_QUERY_RFC3986);
+		$queryString = http_build_query($parameters, '' /* $numeric_prefix */, '&', PHP_QUERY_RFC3986);
 
 		// Payload
 		$amzPayload = array($method);