Unable to display the guest author name

Hi,
When I tried to change the default author name and made to display the actual name given by the guest using the code given by you. It works very fine in my local machine.
But when I tried it in my hosting account it displays the following PHP error message
“Parse error: syntax error, unexpected ‘[‘, expecting ‘)’ “
Please help me on this issue.

https://wordpress.org/plugins/tt-guest-post-submit/