fix broken pyenv on circleci

Author: abarbu

circle.yml

@@ -3,6 +3,7 @@ dependencies:
     - "~/.stack"
     - ".stack-work"
   pre:
+    - rm -rf /opt/circleci/.pyenv
     - curl -sSL https://get.haskellstack.org/ | sh
     - sudo apt-get install -y python3-pip
     - sudo apt-get install -y python3-matplotlib