try to pin down build failures

Author: nicolaskruchten

.circleci/create_conda_optional_env.sh

@@ -16,7 +16,7 @@ if [ ! -d $HOME/miniconda/envs/circle_optional ]; then
     # Create environment
     # PYTHON_VERSION=2.7 or 3.5
     $HOME/miniconda/bin/conda create -n circle_optional --yes python=$PYTHON_VERSION \
-requests nbformat six retrying psutil pandas decorator pytest mock nose poppler xarray scikit-image ipython jupyter ipykernel ipywidgets statsmodels
+requests nbformat six retrying psutil pandas decorator pytest mock nose poppler==0.81.0 xarray scikit-image ipython jupyter ipykernel ipywidgets statsmodels
 
     # Install orca into environment
     $HOME/miniconda/bin/conda install --yes -n circle_optional -c plotly plotly-orca==1.3.1