Use effective-path branch of unipi

This is only temporary in order to test the proposed change.

Dockerfile

@@ -4,7 +4,7 @@ RUN sudo apt update && ( cd opam-repository && git pull origin master ) && opam
     opam install 'mirage>4' && \
     eval $(opam env) && \
     git clone https://github.com/roburio/unipi.git && \
-    ( cd unipi && mirage configure -t spt && make ) && \
+    ( cd unipi && git checkout effective-path && mirage configure -t spt && make ) && \
     { bindir="$(opam var bin)"; cp $bindir/solo5-elftool $bindir/solo5-spt ~/; }
 
 FROM ubuntu:20.04