feat: output ES module build for tools like Rollup

Author: keithamus

.babelrc

@@ -1,7 +1,14 @@
 {
   "plugins": [
     "transform-custom-element-classes",
-    "transform-es2015-modules-umd"
   ],
-  "presets": ["es2015"]
+  "presets": [["es2015", { "modules": false }]],
+  "env": {
+    "umd": {
+      "plugins": [
+        "transform-custom-element-classes",
+        "transform-es2015-modules-umd"
+      ]
+    }
+  }
 }

package.json

@@ -2,6 +2,7 @@
   "name": "include-fragment-element",
   "version": "4.0.1",
   "main": "dist/index-umd.js",
+  "module": "dist/index-es.js",
   "license": "MIT",
   "repository": "github/include-fragment-element",
   "files": [
@@ -11,7 +12,9 @@
     "clean": "rm -rf dist",
     "lint": "eslint include-fragment-element.js test/*.js",
     "prebuild": "npm run clean && npm run lint && mkdir dist",
-    "build": "babel include-fragment-element.js -o dist/index-umd.js",
+    "build": "npm run build-es && npm run build-umd",
+    "build-es": "babel include-fragment-element.js -o dist/index-es.js",
+    "build-umd": "BABEL_ENV=umd babel include-fragment-element.js -o dist/index-umd.js",
     "pretest": "npm run build",
     "test": "karma start ./test/karma.config.js",
     "prepublishOnly": "npm run build"