install tini in the same layer

docker/Dockerfile

@@ -121,15 +121,9 @@ RUN wget --quiet https://repo.continuum.io/miniconda/Miniconda3-py38_${MINICONDA
     'pip' \
     'tini=0.18.0' && \
     conda update --all --quiet --yes && \
-    conda clean --all -f -y && \
-    rm -rf /home/$NB_USER/.cache/yarn && \
-    fix-permissions $CONDA_DIR && \
-    fix-permissions /home/$NB_USER
-
-# Install Tini
-RUN conda install --quiet --yes 'tini=0.18.0' && \
     conda list tini | grep tini | tr -s ' ' | cut -d ' ' -f 1,2 >> $CONDA_DIR/conda-meta/pinned && \
     conda clean --all -f -y && \
+    rm -rf /home/$NB_USER/.cache/yarn && \
     fix-permissions $CONDA_DIR && \
     fix-permissions /home/$NB_USER
 
@@ -140,9 +134,9 @@ RUN conda install --quiet --yes 'tini=0.18.0' && \
 # Do all this in a single RUN command to avoid duplicating all of the
 # files across image layers when the permissions change
 # FIDLE: copy env from fidle
-COPY environment.yml /tmp
+COPY docker/spec-file.txt /tmp
 # FIDLE: update env with environment.yml
-RUN conda env update --name base --quiet --file environment.yml && \
+RUN conda install --name base --file spec-file.txt && \
 #RUN conda install --quiet --yes -n base \
     conda clean --all -f -y && \
 # FIDLE : install jupyterhub via pip