DOC-ONLY: upgrade the "requests" package

requests 2.18.4 is the subject of a security alert

Change-Id: Id1e9338d86bced8c0bb065db7b3dc7f02aa41afc
Signed-off-by: Dave Barach <dave@barachs.net>
diff --git a/docs/etc/requirements.txt b/docs/etc/requirements.txt
index 00f6f09..59b5b8c 100644
--- a/docs/etc/requirements.txt
+++ b/docs/etc/requirements.txt
@@ -24,7 +24,7 @@
 pytz==2018.4
 PyYAML==3.12
 recommonmark==0.4.0
-requests==2.18.4
+requests==2.20.0
 restructuredtext-lint==1.1.3
 singledispatch==3.4.0.3
 six==1.11.0