bump request to 2.19.1 (#3755)

Author: arbll

requirements.txt

@@ -31,7 +31,7 @@ python-etcd==0.4.5
 pyyaml==3.11
 # note: requests is also used in many checks
 # upgrade with caution
-requests==2.19.0
+requests==2.19.1
 # note: simplejson is used in many checks to inteface APIs
 simplejson==3.6.5
 supervisor==3.3.3