Unauthorized: Authentication Required Docker for Mac 1.12

After the reading the solution, I can’t seem to understand what I am wrong. The error message doesn’t tell me what I should be doing to fix the problem

Login with your Docker ID to push and pull images from Docker Hub. If you don't have a Docker ID, head over to https://hub.docker.com to create one.
Username (ngehani): ngehani
Login Succeeded
[neilg@Neil-Gehani-mbp ~/Sites/demo] 11:50:34 $ docker push demo_app
The push refers to a repository [docker.io/library/demo_app]
057c7cc7c58e: Preparing
1561bca9d2fb: Preparing
b15cf904778b: Preparing
b63269c09e76: Preparing
802b40833ec0: Preparing
fc393dfdfc29: Waiting
18bd037aac78: Waiting
e3f9bb01cae2: Waiting
62b890db354a: Waiting
ec0200a19d76: Waiting
338cb8e0e9ed: Waiting
d1c800db26c7: Waiting
42755cf4ee95: Waiting
unauthorized: authentication required```


docker tag <your image> <hub-id>/<your image>:[tag]

and then do docker push