Cleans up some minor issues in cpplint

Summary:

• Corrected typo in install instructions
• Sets the default binary to cpplint.py

Test Plan:

• Running the unit tests.

You may need to check your test environment is set up with the latest
cpplint.py available, since the default binary is being changed.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: Korvin

Maniphest Tasks: T10157

Differential Revision: https://secure.phabricator.com/D15030