Gulp error testing in vsts

Hello internet people,

When I deploy my project to VSTS I get a 255 error.

VSTS error log

var gulp = require('gulp');
var istanbul = require('gulp-istanbul');
var mocha = require('gulp-mocha');


gulp.task('default', ['pre-test'], function() {
    return gulp.src(['test/*.js'])
        .pipe(mocha())
        .pipe(istanbul.writeReports());
});

gulp.task('pre-test', function() {
    return gulp.src(['*.js', 'api/**/*.js', 'auth/**/*.js', 'config/**/*.js'])
        .pipe(istanbul())
        .pipe(istanbul.hookRequire());
});

Does anyone know what the problem is? Thanks in advance.