Fix bug in unit test

[hangxingliu]

1. use --disable-extensions to launch test (avoid test be failure cause other extensions)
2. give more timeout and slow value for Github API test (because network request be sometimes slow)
3. Ignore 403 (API rate limit exceeded) from Github

---

By the way, how to setup Github API token for Travis-CI build: https://docs.travis-ci.com/user/best-practices-security/#Steps-Travis-CI-takes-to-secure-your-data