I get this activation error when I try to active Pro Sites

I get this activation error when I try to active Pro Sites

Parse error: syntax error, unexpected T_PAAMAYIM_NEKUDOTAYIM in /home/sites/restezedigital.com/public_html/wp-content/plugins/pro-sites/pro-sites-files/lib/ProSites/Module/Taxamo/lib/Taxamo/Swagger.php on line 185

Thank,

Jessica