undo python version support update

setup.py

@@ -23,7 +23,7 @@ setup(
     author="Teklia",
     author_email="contact@teklia.com",
     url="https://teklia.com",
-    python_requires=">=3.7",
+    python_requires=">=3.6",
     install_requires=install_requires,
     extras_require={"docs": requirements("docs-requirements.txt")},
     packages=find_packages(),