Add sideEffects to the package json for webpack 4.

__tests__/testIcons.js

@@ -5,8 +5,6 @@ import MuiThemeProvider from 'material-ui/styles/MuiThemeProvider'
 import * as commonjsIcons from '../package/index'
 import * as es2015Icons from '../package/index.es'
 
-console.log('hi')
-
 describe('the generated commonjs module', () => {
   it('should export icons that render to SVGs', () => {
     for (const iconName of Object.keys(commonjsIcons)) {

__tests__/testPackage.js

@@ -0,0 +1,8 @@
+/* eslint-env jest */
+
+describe('the npm package', () => {
+  it('should set sideEffects to false to allow webpack to optimize re-exports', () => {
+    const packageJson = require('../package/package.json')
+    expect(packageJson.sideEffects).toBe(false)
+  })
+})

generate-module.js

@@ -112,6 +112,7 @@ fse.writeFileSync(path.join(__dirname, 'package', 'package.json'), JSON.stringif
   'main',
   'module',
   'jsnext:main',
+  'sideEffects',
   'repository',
   'keywords',
   'author',

package.json

@@ -5,6 +5,7 @@
   "main": "./index.js",
   "module": "./index.es.js",
   "jsnext:main": "./index.es.js",
+  "sideEffects": false,
   "repository": {
     "type": "git",
     "url": "git+https://github.com/TeamWertarbyte/mdi-material-ui.git"