Setup: support python 3.7+ (#37)

Author: adrianeboyd

setup.cfg

@@ -16,7 +16,6 @@ classifiers =
     Operating System :: MacOS :: MacOS X
     Programming Language :: Cython
     Programming Language :: Python :: 3
-    Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
     Programming Language :: Python :: 3.9
@@ -28,7 +27,7 @@ classifiers =
 [options]
 zip_safe = true
 include_package_data = true
-python_requires = >=3.6
+python_requires = >=3.7
 install_requires =
     numpy>=1.21.0
     thinc>=8.1.0,<9.1.0