upgrade requests dependency (#3753)

Author: ofek

requirements.txt

@@ -26,13 +26,12 @@ ntplib==0.3.3
 # utils/service_discovery/config_stores.py
 python-consul==0.4.7
 # utils/service_discovery/config_stores.py
-urllib3<1.23
 python-etcd==0.4.5
 # the libyaml bindings are optional
 pyyaml==3.11
 # note: requests is also used in many checks
 # upgrade with caution
-requests==2.18.4
+requests==2.19.0
 # note: simplejson is used in many checks to inteface APIs
 simplejson==3.6.5
 supervisor==3.3.3