To reproduce:

1.Create new project with collaborate feature.
2.Open that project in newer major version.(For example from 5.4 to 5.5 or 5.5 to 5.6).
3.Make a change to the project.(For example create an empty script).
4.Press on Collab button.
5.Press the provided documentation link about updating Collab project in Collaborate window.

Expected result: Documentation link is forwarded to documentation of the current Unity version opened.
Actual result: Documentation link is forwarded to Unity 5.4 legacy documentation.

Reproduced with 5.4.3f1 to 5.5.1f1, 5.5.1f1 to 5.6.0b8.