In the changelogs in the documentation, WBC support was removed in the 2018-05-25 version. :\ Very unfortunate, many of us are anxiously waiting for the new release for RPI4 and WBC support.
See this link for the change logs: https://docs.emlid.com/navio/common/dev/changelogs/
See this link for our perpetual asking for updates on the new image release: Raspberry Pi 4 support when? - #33 by Mysnomer0