resolve version issue with nglview in Singularity container

nglview requires ipywidgets < 8

container/Singularity

@@ -14,6 +14,7 @@ ln -sf /bin/bash /bin/sh
 # INSTALL SYSTEM DEPS
 #####################
 apt-get update -y && apt-get install -y python3-pip
+pip3 install ipywidgets==7.6.0
 pip3 install nglview \
              ipython \
              jupyter