在TravisCI中为PHP测试启用HipHop语法

How can I enable HipHop syntax for PHP sources when running tests with TravisCI?

I had the error below:

Fatal error: Syntax only allowed in Hack files (<?hh) 
or with -v Eval.EnableHipHopSyntax=true in 
/home/travis/build/Corviz/framework/src/String/StringUtils.php 
on line 20

The project itself is being developed to run primarily with php 7+, so the <?hh is not an option. I could not find anything related until now.

This is my configuration file: https://github.com/Corviz/framework/blob/master/.travis.yml