Upgrade to quantecon-book-theme=0.2.1 (#142)

Author: mmcky

environment.yml

@@ -8,7 +8,7 @@ dependencies:
   - pip:
     - jupyter-book==0.10.2
     - sphinx-multitoc-numbering==0.1.3
-    - quantecon-book-theme==0.2.0
+    - quantecon-book-theme==0.2.1
     - sphinx-tojupyter==0.1.1
     - sphinxext-rediraffe==0.2.7
     - sphinx-exercise==0.1.1