Update golint install instructions
These are the instructions from https://github.com/golang/lint.
The fetch location changed to golang.org/x/lint/golint from github.com/golang/lint/golint.
-u tells go to update the package and its deps if they exist.
-u Shouldn't strictly be necessary, but figured we might as well follow the instructions from golint.
Enable golint without having it installed.
Ensure that the install instructions now show the new location.
Reviewers: epriestley, Blessed Reviewers
Reviewed By: epriestley, Blessed Reviewers
Differential Revision: https://secure.phabricator.com/D21552