Update omniauth-github gem to v1.4.0

[irinkaa]

We had received the following deprecation notice form GitHub:

Hi @pivorak,
On May 14th, 2020 at 16:05 (UTC) your application (pivorak) used an access token (with the User-Agent Faraday v1.0.1) as part of a query parameter to access an endpoint through the GitHub API:
https://api.github.com/user
Please use the Authorization HTTP header instead as using the access_token query parameter is deprecated.
Depending on your API usage, we'll be sending you this email reminder on a monthly basis.
Visit https://developer.github.com/changes/2020-02-10-deprecating-auth-through-query-param for more information about suggested workarounds and removal dates.
Thanks,
The GitHub Team

It seems like this is coming from the omniauth-github gem v1.3.0, and in the v1.4.0 (release notes) this issue is fixed.

We have until September 30, 2020 to upgrade before the brownouts begin.