Adds str fallback to envelope serialization (#1196)

Author: ddeschepper

contrib/opencensus-ext-azure/CHANGELOG.md

@@ -6,6 +6,8 @@
 ([#1187](https://github.com/census-instrumentation/opencensus-python/pull/1187))
 - Modify metrics exporter to include setting export interval to 60s
 ([#1193](https://github.com/census-instrumentation/opencensus-python/pull/1193))
+- Add str fallback to envelope serialization
+([#1196](https://github.com/census-instrumentation/opencensus-python/pull/1196))
 
 ## 1.1.8
 

contrib/opencensus-ext-azure/opencensus/ext/azure/common/transport.py

@@ -113,7 +113,7 @@ def _transmit(self, envelopes):
             endpoint += '/v2.1/track'
             response = requests.post(
                 url=endpoint,
-                data=json.dumps(envelopes),
+                data=json.dumps(envelopes, default=str),
                 headers=headers,
                 timeout=self.options.timeout,
                 proxies=json.loads(self.options.proxies),