Add -update true to command line

Fixes issue #69

Author: thekid

src/main/php/de/thekid/dialog/processing/Videos.php

@@ -97,6 +97,7 @@ public function targets(File $source, ?string $filename= null): iterable {
         '-i', $source->getURI(),
         '-ss', '00:00:03',
         '-vsync', 'vfr',
+        '-update', 'true',
         '-frames:v', '1',
         '-q:v', '1',
         '-qscale:v', '1',