How to reproduce:
1. Open the attached project (Timeline.zip)
2. Open the "SampleScene" Scene
3. In the Hierarchy, select the "Cube" GameObject
4. In the Timeline Window, select the Playable Track
5. In the Inspector Window press the blue documentation button to be directed to its reference page
6. Observe the error message

Expected result: The documentation button directs to the correct reference page
Actual result: The documentation button directs to a dead link (https://docs.unity3d.com/Manual/script-PlayableTrack.htmll)

Reproducable in: 2017.4.0f1, 2017.4.15f1, 2018.1.9f2, 2018.2.16f1, 2018.3.0b10, 2019.1.0a8

Notes: The same is for the Control Track