Fixed 'Failed to verify username.'

Send first request without clientToken, store the returned clientToken, use that for subsequent requests. Dont generate random UUID for clientToken, it can sometimes be 'bad'.
Removed dependency 'uuid'.
Updated 'electron-builder'.

app/assets/js/authmanager.js

@@ -30,6 +30,9 @@ exports.addAccount = async function(username, password){
     try {
         const session = await Mojang.authenticate(username, password, ConfigManager.getClientToken())
         const ret = ConfigManager.addAuthAccount(session.selectedProfile.id, session.accessToken, username, session.selectedProfile.name)
+        if(ConfigManager.getClientToken() == null){
+            ConfigManager.setClientToken(session.clientToken)
+        }
         ConfigManager.save()
         return ret
     } catch (err){

app/assets/js/configmanager.js

@@ -2,7 +2,6 @@ const fs     = require('fs')
 const mkpath = require('mkdirp')
 const os     = require('os')
 const path   = require('path')
-const uuidV4 = require('uuid/v4')
 
 const logger = require('./loggerutil')('%c[ConfigManager]', 'color: #a02d2a; font-weight: bold')
 
@@ -68,7 +67,7 @@ const DEFAULT_CONFIG = {
     },
     commonDirectory: path.join(dataPath, 'common'),
     instanceDirectory: path.join(dataPath, 'instances'),
-    clientToken: uuidV4(),
+    clientToken: null,
     selectedServer: null, // Resolved
     selectedAccount: null,
     authenticationDatabase: {},

app/assets/js/mojang.js

@@ -133,16 +133,21 @@ exports.status = function(){
  */
 exports.authenticate = function(username, password, clientToken, requestUser = true, agent = minecraftAgent){
     return new Promise((resolve, reject) => {
+
+        const body = {
+            agent,
+            username,
+            password,
+            requestUser
+        }
+        if(clientToken != null){
+            body.clientToken = clientToken
+        }
+
         request.post(authpath + '/authenticate',
             {
                 json: true,
-                body: {
-                    agent,
-                    username,
-                    password,
-                    clientToken,
-                    requestUser
-                }
+                body
             },
             function(error, response, body){
                 if(error){