Update quantecon-book-theme to 0.15.1

- Includes fix for path_to_docs stripping in notebook launch URLs
- Colab/JupyterHub/Binder buttons now generate correct URLs for flat notebook repos

Author: mmcky

environment.yml

@@ -7,7 +7,7 @@ dependencies:
   - pip
   - pip:
     - jupyter-book==1.0.4post1
-    - quantecon-book-theme==0.15.0
+    - quantecon-book-theme==0.15.1
     - sphinx-tojupyter==0.3.1
     - sphinxext-rediraffe==0.3.0
     - sphinx-exercise==1.0.1