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/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){