[mod] Upgrade to Poetry v1.1.x

Set poetry-core v1.0.0 as requirement and new build system
https://python-poetry.org/blog/announcing-poetry-1-1-0.html

pyproject.toml

@@ -20,8 +20,8 @@ classifiers = [
 ]
 
 [build-system]
-requires = ["poetry>=0.12"]
-build-backend = "poetry.masonry.api"
+requires = ["poetry-core>=1.0.0"]
+build-backend = "poetry.core.masonry.api"
 
 [tool.poetry.dependencies]
 python = "^3.6.8"