gulpfile.js

function lintJson() {
  return gulp.src('*.theme.json')
    .pipe(jsonlint())
    .pipe(jsonlint.reporter());
}

gulp.task('validate:json', 'Test JSON', function() {
  return lintJson().pipe(jsonlint.failAfterError());
});
tasks.validate.push('validate:json');

gulp.task('lint:json', function() {
  return lintJson();
});
gulp.task('watch:json', 'Watch JSON to lint', ['validate:json'], function() {
  return gulp.watch('*.theme.json', ['lint:json']);
});
tasks.watch.push('watch:json');