var ops = [
            {
                path: "/fields/System.Title",
                op: "add",
                value: "Hello world"
            }
        ];

    var options = {
        url: 'http://localhost:8080/tfs/DefaultCollection/Agile Git/_apis/wit/workItems/$Bug?api-version=2.2',
        username: 'username',
        password: 'password',
        domain: 'domain',
        method: 'PATCH',
        headers: {
          'Content-Type': 'application/json-patch+json'
        },
        body: JSON.stringify(ops)
    };

    httpntlm.patch(options, function(err,res) {
                console.log("patch complete");
                console.log(res.body);
    })