Links inside docs page after staticpkg are broken

[dwaw18]

Describe the bug
After running staticpkg, attempt to navigate inside docs page fails (404 - page not found).

To Reproduce
Steps to reproduce the behavior:

1. Run pxt staticpkg and http-server -c-1 built/packaged in custom pxt target
2. Go to http://localhost:8080/docs/blocks/loops.html
3. Click on any of present blocks.
4. See 404 error - page not found.

Expected behavior
Docs about given block should be displayed properly.

Desktop (please complete the following information):

• OS: Windows 10
• Browser: Google Chrome
• Version: 69.0.3497.100

Additional context

• pxt-core version: 4.0.5
• When directly opening http://localhost:8080/docs/blocks/loops/for.html, page is displayed correctly.
• To my understanding, only links associated to blocks are broken, because when I click on for link in See also section, page is displayed properly. Navigating through left=hand side menu also seems to work fine.

[FranklinWhale]

May be related to #4700 (comment)

[guillaumejenkins]

This should have been fixed by #4704

[dwaw18]

There is definitely an improvement, but for example clicking on for block in loops category is still causing a 404 error.