remove conda history file

seems to result in unintended pinning of packages installed when setting up base env

repo2docker/buildpacks/conda/install-miniconda.bash

@@ -57,8 +57,12 @@ if [[ -f /tmp/kernel-environment.yml ]]; then
 
     conda env create -n kernel -f /tmp/kernel-environment.yml
     ${CONDA_DIR}/envs/kernel/bin/ipython kernel install --prefix "${CONDA_DIR}"
+    rm -f ${CONDA_DIR}/envs/kernel/conda-meta/history
 fi
-
+# remove conda history file,
+# which seems to result in some effective pinning of packages in the initial env,
+# which we don't intend
+rm -f ${CONDA_DIR}/conda-meta/history
 # Clean things out!
 conda clean -tipsy