[EN-2047] cython again in build-system

Author: iamishalkin

pyproject.toml

@@ -60,5 +60,5 @@ post_build = 'task clear'
 post_test = 'task clear'
 
 [build-system]
-requires = ['poetry_core>=1.0.0', 'setuptools']
+requires = ['poetry_core>=1.0.0', 'setuptools', 'cython']
 build-backend = 'poetry.core.masonry.api'