Messages

I click on the upgrade link given in the admin notice and accepted the risk of the upgrade.
The page when blank
Then the error "Parse error: syntax error, unexpected ':', expecting ';' or '{' in /home/onlinesr/public_html/test3/core/lib/PaymentHandlerInterface.php on line 22" when I try to access my site.

What's wrong?
Luckily it was a plain vanilla test site which I've installed from cpanel just a day before.