pin poetry to 1.1.15 (#241)

* pin poetry to 1.1.5

* change poetry version in test.yaml

* try poetry 1.1.5

* use 1.1.15 not 1.1.5

Author: Dr-Irv

.github/workflows/test.yml

@@ -22,7 +22,7 @@ jobs:
         python-version: ${{ matrix.python-version }}
 
     - name: Install Poetry
-      run: pip install poetry
+      run: pip install poetry==1.1.15
 
     - name: Determine poetry version
       run: echo "::set-output name=VERSION::$(poetry --version)"