[docker] add safe directory which can allow git diff

docker/Dockerfile.master

@@ -22,6 +22,7 @@ RUN adduser --disabled-password \
 USER root
 RUN chown -R ${NB_UID} ${HOME}
 RUN chmod -R +r /opt/openfpga/
+git config --global --add safe.directory *
 USER ${NB_USER}
 
 WORKDIR ${HOME}