fix: only allow installs from the main process

BREAKING CHANGE

README.md

@@ -23,30 +23,24 @@ yarn add electron-devtools-installer -D
 ```
 
 ## Usage
-In your `electron-starter.js` file, add the following callback to `app.on('ready', ... )`,
+All you have to do now is this in the **main** process of your application.
 
 ```js
-const { default: installExtension, REDUX_DEVTOOLS } = require('electron-devtools-installer');
-const { app, BrowserWindow } = require('electron');
+import installExtension, { REDUX_DEVTOOLS } from 'electron-devtools-installer';
+// Or if you can not use ES6 imports
+/**
+const { default: installExtension, REACT_DEVELOPER_TOOLS } = require('electron-devtools-installer');
+*/
+const { app } = require('electron');
 
-app.on('ready', () => {
+app.whenReady().then(() => {
     installExtension(REDUX_DEVTOOLS)
         .then((name) => console.log(`Added Extension:  ${name}`))
         .catch((err) => console.log('An error occurred: ', err));
 });
 ```
 To install multiple extensions, `installExtension` takes an array.
 
-Alternatively, using `require()` and destructuring (node v6 or higher) you can
-
-```js
-const { default: installExtension, REACT_DEVELOPER_TOOLS } = require('electron-devtools-installer');
-
-installExtension(REACT_DEVELOPER_TOOLS)
-    .then((name) => console.log(`Added Extension:  ${name}`))
-    .catch((err) => console.log('An error occurred: ', err));
-```
-
 ## What extensions can I use?
 
 Technically you can use whatever extension you want.  Simply find the ChromeStore ID

src/utils.js

@@ -1,4 +1,4 @@
-import electron, { remote } from 'electron';
+import { net } from 'electron';
 import fs from 'fs';
 import path from 'path';
 import https from 'https';
@@ -9,22 +9,26 @@ export const getPath = () => {
 };
 
 // Use https.get fallback for Electron < 1.4.5
-const { net } = remote || electron;
 const request = net ? net.request : https.get;
 
-export const downloadFile = (from, to) =>
-  new Promise((resolve, reject) => {
+export const downloadFile = (from, to) => {
+  if (process.type !== 'browser') {
+    return Promise.reject(new Error('electron-devtools-installer can only be used from the main process'));
+  }
+  return new Promise((resolve, reject) => {
     const req = request(from);
     req.on('response', (res) => {
       // Shouldn't handle redirect with `electron.net`, this is for https.get fallback
       if (res.statusCode >= 300 && res.statusCode < 400 && res.headers.location) {
         return downloadFile(res.headers.location, to).then(resolve).catch(reject);
       }
       res.pipe(fs.createWriteStream(to)).on('close', resolve);
+      res.on('error', reject);
     });
     req.on('error', reject);
     req.end();
   });
+}
 
 export const changePermissions = (dir, mode) => {
   const files = fs.readdirSync(dir);