Problem in Rebuild Search Index

Dear All,
I can’t re-generate the index following command php tools/rebuildSearchIndex.php, and showing this error.

Version- 3.1.1.4

PHP Parse error: syntax error, unexpected ‘[’ in /var/www/vhosts/journals.co/journalsci.com/lib/pkp/lib/vendor/nikic/fast-route/src/functions.php on line 12

I m use dedicated server

Regards,
Surojit Bera