Change build folders to es & cjs

This will make importing the es module a little nicer:

  import Waypoint from 'react-waypoint/es';

instead of

  import Waypoint from 'react-waypoint/build/index.mjs';

Thanks to @jmeas for the suggestion.

.eslintignore

@@ -1 +1,3 @@
 build
+es
+cjs

.gitignore

@@ -1,4 +1,6 @@
 build
+es
+cjs
 node_modules
 npm-debug.log
 .idea/

README.md

@@ -47,7 +47,7 @@ import Waypoint from 'react-waypoint';
 ```
 
 *Alternatively, you can also use the ES module that this package provides:
-`import Waypoint from 'react-waypoint/build/index.mjs'`.*
+`import Waypoint from 'react-waypoint/es'`.*
 
 A waypoint normally fires `onEnter` and `onLeave` as you are scrolling, but it
 can fire because of other events too:

package.json

@@ -2,7 +2,7 @@
   "name": "react-waypoint",
   "version": "7.3.0",
   "description": "A React component to execute a function whenever you scroll to an element.",
-  "main": "build/index.js",
+  "main": "cjs/index.js",
   "types": "index.d.ts",
   "repository": {
     "type": "git",
@@ -14,7 +14,7 @@
     "build": "npm run clean && rollup -c",
     "check-changelog": "expr $(git status --porcelain 2>/dev/null| grep \"^\\s*M.*CHANGELOG.md\" | wc -l) >/dev/null || (echo 'Please edit CHANGELOG.md' && exit 1)",
     "check-only-changelog-changed": "(expr $(git status --porcelain 2>/dev/null| grep -v \"CHANGELOG.md\" | wc -l) >/dev/null && echo 'Only CHANGELOG.md may have uncommitted changes' && exit 1) || exit 0",
-    "clean": "rimraf build",
+    "clean": "rimraf es cjs",
     "lint": "eslint . --ext .js,.jsx",
     "postversion": "git commit package.json CHANGELOG.md -m \"Version $npm_package_version\" && npm run tag && git push && git push --tags && npm publish",
     "prepublish": "in-publish && safe-publish-latest && npm run build || not-in-publish",

rollup.config.js

@@ -10,7 +10,7 @@ export default [
     ],
     output: [
       { file: pkg.main, format: 'cjs' },
-      { file: 'build/index.mjs', format: 'es' }
+      { file: 'es/index.mjs', format: 'es' }
     ],
     plugins: [
       babel({