Test sphinx 1.5.6

Author: qinezh

appveyor.yml

@@ -13,7 +13,7 @@ environment:
 install:
   - SET PATH=%PYTHON%;%PYTHON%\Scripts;%PATH%
   - python scripts/dev_setup.py
-  - python -m pip install sphinx
+  - python -m pip install sphinx==1.5.6
 
 build_script:
   - ps: |