Set minimum python version in setup.py to 3.7, as 3.6 is not actually supported anymore

Author: Tim Schneider

setup.py

@@ -78,6 +78,6 @@ def build_extension(self, ext):
         "Programming Language :: C++",
     ],
     install_requires=["numpy"],
-    python_requires=">=3.6",
+    python_requires=">=3.7",
     zip_safe=False,
 )