Change login module to use gh-get-token

[icyflame]

First, fix icyflame/node-gh-get-token#1

Then use http://npmjs.com/package/gh-get-token

[Saurabh3333]

After using gh-get-token for login, I am getting:
Existing token returned!
Visit https://github.com/settings/developers in your browser to revoke access.

Is it what we are expecting?

[icyflame]

Yeah, if there is an existing token for this application, gh-get-token will return the same token. That's how the GitHub api works. (You may have to activate 2 factor authentication to test this feature properly)