CIRCLE Revert to sphinx 1.5

to fix pdf doc generation

build_tools/circle/build_doc.sh

@@ -88,7 +88,7 @@ sudo -E apt-get -yq update
 sudo -E apt-get -yq remove texlive-binaries --purge
 sudo -E apt-get -yq --no-install-suggests --no-install-recommends --force-yes \
     install dvipng texlive-latex-base texlive-latex-extra \
-    texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended latexmk
+    texlive-latex-recommended texlive-latex-extra texlive-fonts-recommended
 
 # deactivate circleci virtualenv and setup a miniconda env instead
 if [[ `type -t deactivate` ]]; then
@@ -105,7 +105,7 @@ conda update --yes --quiet conda
 # Configure the conda environment and put it in the path using the
 # provided versions
 conda create -n $CONDA_ENV_NAME --yes --quiet python numpy scipy \
-  cython nose coverage matplotlib sphinx pillow
+  cython nose coverage matplotlib sphinx=1.5 pillow
 source activate testenv
 
 # Build and install scikit-learn in dev mode