gulpfile.js

var jsonFiles = ['*.theme.json'];

// Setup the linting
function lintJson() {
  return gulp.src(jsonFiles)
    .pipe(jsonlint())
    .pipe(jsonlint.reporter());
}

// Add a validate task that will fail on lint error
gulp.task('validate:json', 'Test JSON', function() {
  return lintJson().pipe(jsonlint.failAfterError());
});
tasks.validate.push('validate:json');

// Add a lint task
gulp.task('lint:json', lintJson);

// Run the lint tasks on the watched files
gulp.task('watch:json', 'Watch JSON', ['lint:json'], function() {
  return gulp.watch(jsonFiles, ['lint:json']);
});
tasks.watch.push('watch:json');