Unnoticed error generation

[shreyass-ranganatha]

File: ed_analytics/github.py
Method: Repository.get_commits()

the function get_commits() fails to check the request's response code, and hence tries to work with whatever response comes out. Need an implementation for a check for response code and a thoughtful work through further

[shreyass-ranganatha]

Example; when GitHub REST API requests reach a rate-limit, the error risen would be "TypeError: list indices must be integers or slices, not str."

We need it to specify the message that GitHub REST API poses