fix: name conflict with other exemplars

The venv cannot be named recode, since a student might be working
through multiple exemplars which would lead to name conflicts
for the venvs.

I named the conda venv mcmc for Monte Carlo Markov Chain.

environment.yml

@@ -1,4 +1,4 @@
-name: recode
+name: mcmc
 
 channels:
   - defaults