add a version check, the third argument in getopt requires PHP >= 7.1

bin/migrate

@@ -10,6 +10,10 @@ require PATH . 'vendor' . DIRECTORY_SEPARATOR . 'autoload.php';
 use PrivateBin\Configuration;
 use PrivateBin\Model;
 
+// third argument in getopt requires PHP >= 7.1
+if (version_compare(PHP_VERSION, '7.1.0') < 0) {
+    dieerr('migrate requires php 7.1 or above to work. Sorry.');
+}
 
 $longopts = array(
     "delete-after",