CI Install psutil (scikit-learn#6897)

Author: raghavrv

build_tools/circle/build_doc.sh

@@ -45,7 +45,7 @@ popd
 # Configure the conda environment and put it in the path using the
 # provided versions
 conda create -n testenv --yes --quiet python numpy scipy \
-  cython nose coverage matplotlib sphinx pillow
+  cython nose coverage matplotlib sphinx pillow psutil
 source /home/ubuntu/miniconda/envs/testenv/bin/activate testenv
 
 # Build and install scikit-learn in dev mode