GITHUB_ACCESS_TOKEN environment variable is never used #406

Even though it's set in the environment, I always get this error when trying to run oss-health against something hosted in github:

WARN - Unable to calculate health for pkg:github/stevemao/left-pad: Missing GitHub access token. Please define GITHUB_ACCESS_TOKEN.
I think I have found the reason and will submit a PR shortly, but may be the wrong way to fix it, as I am new to c# or this project.