bump version to 1.6.0
bump version to 1.6.0

Change-Id: I1f989b800d93ed2e9110ac719781b8f32ca64e77
Reviewed-on: https://gerrit.instructure.com/90200
Tested-by: Jenkins
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Product-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>
QA-Review: Simon Williams <088e16a1019277b15d58faf0541e11910eb756f6@instructure.com>

instructure/switchman,instructure/switchman