Add quantecon-book-theme PR #322 to testing

- Install quantecon-book-theme from PR #322
- Now testing both sphinx-exercise PR #81 and theme PR #322
- Related: QuantEcon/quantecon-book-theme#322

Author: mmcky

environment.yml

@@ -7,7 +7,7 @@ dependencies:
   - pip
   - pip:
     - jupyter-book==1.0.4post1
-    - quantecon-book-theme==0.10.0
+    - quantecon-book-theme @ git+https://github.com/QuantEcon/quantecon-book-theme.git@refs/pull/322/head
     - sphinx-tojupyter==0.3.1
     - sphinxext-rediraffe==0.2.7
     - sphinx-exercise @ git+https://github.com/executablebooks/sphinx-exercise.git@refs/pull/81/head