Upgrade New Relic plugin

We're seeing an error in sending to the collector, there are also
a number of changes.
https://docs.newrelic.com/docs/release-notes/agent-release-notes/python-release-notes

requirements/edx/base.txt

@@ -132,7 +132,7 @@ watchdog==0.8.3
 
 # Metrics gathering and monitoring
 dogapi==1.2.1
-newrelic==2.74.0.54
+newrelic==2.78.0.57
 
 # Used for documentation gathering
 sphinx==1.1.3