reverting back to r3.6.3 for all-spark-notebook

all-spark-notebook/Dockerfile

@@ -23,7 +23,7 @@ USER $NB_UID
 
 # R packages
 RUN conda install --quiet --yes \
-    'r-base=4.0.0' \
+    'r-base=3.6.3' \
     'r-ggplot2=3.3*' \
     'r-irkernel=1.1*' \
     'r-rcurl=1.98*' \
@@ -48,4 +48,4 @@ RUN conda install --quiet --yes 'spylon-kernel=0.4*' && \
     python -m spylon_kernel install --sys-prefix && \
     rm -rf /home/$NB_USER/.local && \
     fix-permissions $CONDA_DIR && \
-    fix-permissions /home/$NB_USER
+    fix-permissions /home/$NB_USER
\ No newline at end of file