Test github-token to see if it is valid before using it

[NobodyXu]

We can use:

curl --request GET \
       --url "https://api.github.com/octocat" \
       --header "Authorization: Bearer YOUR-TOKEN"

to test the github-token before using it and possibly print a warning and drop it to fallback to unauthorized mode
if the token is invalid.

[passcod]

We can also test for the gh*_ prefix as an early check.

[NobodyXu]

Aha right, this is the most simple check we can get.