Bug 1158212 - Update New Relic Python agent to v2.50.0.39

v2.44.0.36 (11th Feb) -> v2.50.0.39 (6th April)

Brings improvements to SQL reporting, Django 1.8 support, improved
perf/resource usage in some cases.

For more info see:
https://docs.newrelic.com/docs/release-notes/agent-release-notes/python-release-notes

requirements/prod.txt

@@ -1,2 +1,2 @@
-# sha256: Nz068-nwwjOTLdzwJPl47tO9bOrulWOu22XAKff5src
-newrelic==2.44.0.36
+# sha256: _d1HqNBI4MX0Lu5RGoqvNYkcmW1slZVTx77Is6x0s8s
+newrelic==2.50.0.39