gulp.clean.js

var fs = require('fs'),
    del = require('del');

gulp.task('clean', function(done) {

  var files = fs.readdirSync('dist');
  var targets = [];

  if(files.length) {
    targets.push('dist/*');
  }

  if(fs.existsSync('your-file.js')) {
    targets.push('your-file.js');
  }

  if(targets.length) {
    return del(targets);
  } else {
    done();
    console.log('Delete directory and file not found.');
  }

});