Missing github token in travis

[lwsanty]

--- SKIP: TestGitHubSkipForks (0.00s)
    github_test.go:94: test running on travis CI but couldn't find GITHUB_TOKEN
PASS

https://travis-ci.com/src-d/gitcollector/jobs/235932304

[lwsanty]

https://github.com/src-d/infrastructure/issues/1154#issuecomment-532596435