Using gulp script with template strings (backtick)

https://travis-ci.com/github/cerbaire/Foobar2000/builds/164526936

Hello,

In my build script I call gulp. In my gulp script, I use template strings (string using backtick with variable inside). Doing this generate the following error :
/home/travis/build/cerbaire/Foobar2000/DUiTunes_SMP/gulpfile.js:50
const headerComment = // Built ${new Date().toISOString()}\n;
^
SyntaxError: Unexpected token ILLEGAL
at Module._compile (module.js:439:25)
at Object.Module._extensions…js (module.js:474:10)
at Module.load (module.js:356:32)
at Function.Module._load (module.js:312:12)
at Module.require (module.js:364:17)
at require (module.js:380:17)
at execute (/home/travis/build/cerbaire/Foobar2000/DUiTunes_SMP/node_modules/gulp-cli/lib/versioned/^4.0.0/index.js:36:18)
at Liftoff.handleArguments (/home/travis/build/cerbaire/Foobar2000/DUiTunes_SMP/node_modules/gulp-cli/index.js:201:24)
at Liftoff.execute (/home/travis/build/cerbaire/Foobar2000/DUiTunes_SMP/node_modules/gulp-cli/node_modules/liftoff/index.js:201:12)
at module.exports (/home/travis/build/cerbaire/Foobar2000/DUiTunes_SMP/node_modules/gulp-cli/node_modules/liftoff/node_modules/flagged-respawn/index.js:51:3)

Thanks for your help