Upgrading server dependancies (#6431)

vendor/github.com/minio/minio-go/utils.go

@@ -110,6 +110,8 @@ func closeResponse(resp *http.Response) {
 	}
 }
 
+var emptySHA256 = sum256(nil)
+
 // Sentinel URL is the default url value which is invalid.
 var sentinelURL = url.URL{}