build: use lighter poetry-core

Author: branchv

pyproject.toml

@@ -47,5 +47,5 @@ known_first_party = "hypothesis_graphql"
 known_third_party =["attr", "graphql", "hypothesis", "hypothesis_graphql", "pytest"]
 
 [build-system]
-requires = ["poetry>=0.12"]
-build-backend = "poetry.masonry.api"
+requires = ["poetry-core>=1.0"]
+build-backend = "poetry.core.masonry.api"