Add esm module distribution

Author: mtorromeo

package.json

@@ -3,6 +3,7 @@
  "version": "3.5.0",
  "description": "Async computed properties for Vue",
  "main": "dist/vue-async-computed.js",
+ "module": "dist/vue-async-computed.esm.js",
  "files": [
  "bin/",
  "dist/"
@@ -14,8 +15,9 @@
  "watch": "watch 'npm run build' src test",
  "test": "babel-node --presets env test/index.js | tspec",
  "prebuild": "npm run check -s && npm run clean -s && mkdirp dist",
- "build": "npm run rollup -s && npm run babel -s",
- "rollup": "rollup src/index.js --output.format umd --name AsyncComputed --output.file dist/vue-async-computed.esnext.js",
+ "build": "npm run rollup-esm -s && npm run rollup-umd -s && npm run babel -s",
+ "rollup-esm": "rollup src/index.js --output.format esm --name AsyncComputed --output.file dist/vue-async-computed.esm.js",
+ "rollup-umd": "rollup src/index.js --output.format umd --name AsyncComputed --output.file dist/vue-async-computed.esnext.js",
  "babel": "babel --optional runtime dist/vue-async-computed.esnext.js --out-file dist/vue-async-computed.js",
  "postbuild": "npm run test -s",
  "coverage": "node_modules/.bin/babel-node node_modules/.bin/babel-istanbul cover test/index.js",