docs/requirements.txt: add typing_extensions

anthrotype · anthrotype · commit b4a88ff21b58 · 2020-04-29T19:30:16.000+01:00
pip-compile doesn't support environment markers..
diff --git a/docs/requirements.txt b/docs/requirements.txt
@@ -1,3 +1,4 @@
 -r ../requirements.txt
+typing_extensions; python_version < '3.8'
 sphinx>3
 sphinx_rtd_theme
