FIX: Add sphinx

Author: larsoner

environment.yml

@@ -16,6 +16,8 @@ dependencies:
 - pytest-cov
 - flake8
 - pygments
+- sphinx
+- numpydoc
 - pip:
   - "https://api.github.com/repos/enthought/traits/zipball/a99b3f64d50c5f7f28ffc01bf69419b061f9e976"
   - "https://api.github.com/repos/enthought/pyface/zipball/6a0cac149d56293482bb828a7d98122667c773be"
@@ -26,3 +28,4 @@ dependencies:
   - pytest-faulthandler
   - imageio
   - codecov
+  - sphinx-gallery