Running "git checkout WeBWorK-2.17+" leaves you in a detached state. You can't pull once you do that. Run "git checkout -b WeBWorK-2.17+ WeBWorK-2.17+" to check out the WeBWorK-2.17+ tag to the local branch that is also named WeBWorK-2.17+. You won't need to pull because it will already be up to date. However, pull will work, it will just tell you your branch is up to date.
Installation
Webwork2.16 Update to 2.17 (unable to access git)
This forum has a limit to the number of forum postings you can make in a given time period - this is currently set at 5 posting(s) in 1 day