I was facing same problem and here is what I did that worked for me.
Use ssh instead of http. Remove origin if its http.
git remote rm origin
Add ssh url
git remote add origin git@github.com:<username>/<repo>.git
Generate ssh key inside .ssh/ folder. It will ask for path and passphrase where you can just press enter and proceed.
cd ~/.ssh
ssh-keygen
Copy the key. You can view your key using –
cat ~/.ssh/id_rsa.pub
If you hadn’t specified a different path then this will be the default path.
Add this key to your github account.
Next do –
ssh -T git@github.com
You will get a welcome message in your console.
cd into to your project folder. git push -u origin master now works!