Update requests from 2.20.1 to 2.21.0

requirements/docs.txt

@@ -63,9 +63,9 @@ pytz==2018.7 \
     --hash=sha256:8e0f8568c118d3077b46be7d654cc8167fa916092e28320cde048e54bfc9f1e6 \
     --hash=sha256:31cb35c89bd7d333cd32c5f278fca91b523b0834369e757f4c5641ea252236ca
 # requests is required by Sphinx
-requests==2.20.1 \
-    --hash=sha256:65b3a120e4329e33c9889db89c80976c5272f56ea92d3e74da8a463992e3ff54 \
-    --hash=sha256:ea881206e59f41dbd0bd445437d792e43906703fff75ca8ff43ccdb11f33f263
+requests==2.21.0 \
+    --hash=sha256:7bf2a778576d825600030a110f3c0e3e8edc51dfaafe1c146e39a2027784957b \
+    --hash=sha256:502a824f31acdacb3a35b6690b5fbf0bc41d63a24a45c4004352b0242707598e
 sphinxcontrib-httpdomain==1.7.0 \
     --hash=sha256:1fb5375007d70bf180cdd1c79e741082be7aa2d37ba99efe561e1c2e3f38191e \
     --hash=sha256:ac40b4fba58c76b073b03931c7b8ead611066a6aebccafb34dc19694f4eb6335