Install jupyterlite-sphinx from a commit hash to get jupyterlite/jupyterlite-sphinx#24

When jupyterlite-sphinx is released, we can go back to installing from pypi.

Author: jasongrout

docs/environment.yml

@@ -18,5 +18,7 @@ dependencies:
 
   - pip:
     - ..
-    - jupyterlite-sphinx
+    # Until jupyterlite-sphinx>0.4.9 is released, install from a commit hash to get the jupyterlite_contents config option
+    # - jupyterlite-sphinx
+    - https://github.com/jupyterlite/jupyterlite-sphinx/archive/944ccf4ee977627dbf75b5ae1994c08718566c76.zip
     - jupyterlite>=0.1.0b9