Pin conda version to $CONDA_VERSION

Pin the conda version so that a call to `conda update --all` will not
cause conda to update itself to a higher version with possible breaking
changes.

Motivating example: Upgrade from __4.6.*__ to __4.7.5__ causes the build to fail
due to a conda error:

    [Errno 13] Permission denied: '/.cph_tmpilpdzq7x'

Resolves #891

base-notebook/Dockerfile

@@ -67,17 +67,18 @@ RUN mkdir /home/$NB_USER/work && \
 
 # Install conda as jovyan and check the md5 sum provided on the download site
 ENV MINICONDA_VERSION=4.5.12 \
-    CONDA_VERSION=4.6.7
+    CONDA_VERSION=4.6.14
 
 RUN cd /tmp && \
     wget --quiet https://repo.continuum.io/miniconda/Miniconda3-${MINICONDA_VERSION}-Linux-x86_64.sh && \
     echo "866ae9dff53ad0874e1d1a60b1ad1ef8 *Miniconda3-${MINICONDA_VERSION}-Linux-x86_64.sh" | md5sum -c - && \
     /bin/bash Miniconda3-${MINICONDA_VERSION}-Linux-x86_64.sh -f -b -p $CONDA_DIR && \
     rm Miniconda3-${MINICONDA_VERSION}-Linux-x86_64.sh && \
+    echo "conda ${CONDA_VERSION}" >> $CONDA_DIR/conda-meta/pinned && \
     $CONDA_DIR/bin/conda config --system --prepend channels conda-forge && \
     $CONDA_DIR/bin/conda config --system --set auto_update_conda false && \
     $CONDA_DIR/bin/conda config --system --set show_channel_urls true && \
-    $CONDA_DIR/bin/conda install --quiet --yes conda="${CONDA_VERSION%.*}.*" && \
+    $CONDA_DIR/bin/conda install --quiet --yes conda && \
     $CONDA_DIR/bin/conda update --all --quiet --yes && \
     conda list python | grep '^python ' | tr -s ' ' | cut -d '.' -f 1,2 | sed 's/$/.*/' >> $CONDA_DIR/conda-meta/pinned && \
     conda clean --all -f -y && \