Remove GITHUB_TOKEN from token.js

[alexbbt]

Description

Remove the GITHUB_TOKEN from token.js, Instead it should only use the project specific BUNDLESIZE_GITHUB_TOKEN

Motivation and Context

This was causing an error with generic CI tokens, #93

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code follows the code style of this project.
• If my change requires a change to the documentation I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I created an issue for the Pull Request

[reznord]

I'm afraid this might break for the people who are using github_token.

cc @siddharthkp

[alexbbt]

@reznord Could they not change the name of their variable?

[siddharthkp]

Sorry, have to say no to this to keep old builds working.

Could they not change the name of their variable?

They could, but

1. communicating that change is hard. It will have to be a major version release and mentioned in the change log for folks upgrading
2. it's a very small convenience that the library can absorb without requiring a change from all its users