gulpfile.babel.js

import gulp from 'gulp';
import ts from 'gulp-typescript';
import babel from 'gulp-babel';

gulp.task('build', () => {
  return gulp.src(['typings/tsd.d.ts', 'src/**/*.ts'])
    .pipe(ts({
        target: 'ES6',
        outDir: 'build'
    }))
    .pipe(babel())
    .pipe(gulp.dest('build'))
  ;
});