chore(ci): update appveyor test environment

Update to run against Python 3.x instead of EOL 2.x

Signed-off-by: Mike Fiedler <miketheman@gmail.com>

Author: miketheman

appveyor.yml

@@ -1,8 +1,8 @@
 version: '{build}'
 init:
-    - cmd: python -m pip install -U pip
-    - cmd: pip install pipenv
-    - cmd: pip install poetry==1.0.0a2
+    - cmd: python3 -m pip install -U pip
+    - cmd: pip3 install pipenv
+    - cmd: pip3 install poetry
     - cmd: npm i -g serverless
 build: off
 test_script: