MAINT: Update quantecon environment

Author: mmcky

environment.yml

@@ -14,7 +14,8 @@ dependencies:
     - ghp-import==1.1.0
     - sphinxcontrib-youtube==1.1.0
     - sphinx-togglebutton==0.3.1
-    # Sandpit
+    # Sandpit Requirements
+    - quantecon
     - array-to-latex
     - PuLP
     - cvxpy