Only use stable releases for tests

.appveyor.yml

@@ -16,7 +16,7 @@ install:
   - "python -m pip install --disable-pip-version-check --user --upgrade pip"
 
   # Create poetry virtualenv
-  - "python -m pip install poetry --pre"
+  - "python -m pip install poetry"
 
   # Install dependencies
   - "poetry install -v"

.travis.yml

@@ -11,7 +11,7 @@ cache:
     - $HOME/.cache/pre-commit
 
 install:
-  - pip install poetry --pre
+  - pip install poetry
   - poetry install -v
 
 script: pytest -q tests/