Use public_repo instead of repo when generating OAuth token

`repo' allows access to both public and private repositories,
whereas `public_repo' allows only public repositories.
Change icon for tests that passed
Merge pull request #151 from mattpap/public_repo

Use public_repo instead of repo when generating OAuth token

There is no reason for SymPy Bot to have access to private repositories.
Merge pull request #157 from idlike2dream/icon

Change icon for tests that passed