don't cache invalid credentials

[warner]

In sigma/magit-gh-pulls#5 (comment) I noticed that gh.el can cached a stale (invalid) oauth token from my ~/.gitconfig file, and I couldn't find any way to clear it. Eventually I had to quit emacs entirely and start it up again.

It'd be nice if the credential were only cached after it had been seen to work properly, or maybe the cache could be automatically invalidated if the library ever gets a bad-auth error.

[aspiers]

I saw this too. However you don't need to restart emacs; it's sufficient to eval (defvar gh-auth-alist nil).