Pin TO builder golang version to 1.11.13 (#3957)
Pin TO builder golang version to 1.11.13 (#3957)

Golang versions > 1.11 seem to break the TO-Riak communication channel
for some reason. Pin the version used to build TO-Go to 1.11 until we
have triaged the TO-Riak issues and are able to use golang > 1.11.
hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol,hbeatty/incubator-trafficcontrol