Install requirements in RTD (aio-libs#3224)

webknjaz · web-flow · commit 1325fd9b82a1 · 2018-08-28T13:30:15.000+02:00
Fixes aio-libs#3221 Ref: https://docs.rtfd.io/en/latest/yaml-config.html
diff --git a/.readthedocs.yml b/.readthedocs.yml
@@ -3,3 +3,4 @@ build:
 python:
   version: 3.6
   pip_install: true
+requirements_file: requirements/cython.txt
