target symlinks break mdbook build on windows

[hlavaatch]

Please remove the target symlinks, they break mdbook build on windows.

C:\Users\hlavac\Desktop\discovery>mdbook build
2021-02-06 23:56:38 [INFO] (mdbook::book): Book building has started
2021-02-06 23:56:38 [INFO] (mdbook::book): Running the html backend
2021-02-06 23:56:39 [ERROR] (mdbook::utils): Error: Rendering failed
2021-02-06 23:56:39 [ERROR] (mdbook::utils):    Caused By: Failed to read "C:\\Users\\hlavac\\Desktop\\discovery\\src\\05-led-roulette\\target"
2021-02-06 23:56:39 [ERROR] (mdbook::utils):    Caused By: Access is denied. (os error 5)

When I remove the symlinks, mdbook works OK.