Syncing up with upstream version cambridgehackers:master

Go to the Forked Repo (yours) and just click green button.
It will show you "switching base" message button. click it.
Now it will automatically lead to your original repo. write some commit message and Click Create Pull Request button.
Now it will lead to your forked repo automatically, click Merge pull request and Confirm merge to finish.

To make long story short, In your forked repo, just click green button, switching base button, then green button, green button, and green button.