circle: add dipy install so that build docs do not fail

Author: oesteban

docker/nipype_test_py27/Dockerfile

@@ -51,6 +51,7 @@ RUN mkdir -p /root/src/nipype
 COPY . /root/src/nipype
 
 RUN cd /root/src/nipype && \
+    pip install dipy && \
     pip install -r requirements.txt && \
     pip install -e .