enable debugging

Dockerfile

@@ -104,7 +104,7 @@ USER root
 RUN chown -R $NB_USER:$NB_GID $PWD
 USER $NB_USER
 
-RUN python make -v cpp --include-path /usr/include/gsl/ --library-path /usr/lib/ 
+RUN python make -v --debug cpp --include-path /usr/include/gsl/ --library-path /usr/lib/ 2>&1
 
 RUN python make -v python --include-path /usr/include/gsl/ --library-path /usr/lib/