Fixed DataDog trace exporter

`ddtrace` package introduced some breaking changes that break the
DataDog trace exporter. This commit downgrades the dependency to last
know working version to fix the exporter.

Author: owais

exporter/opentelemetry-exporter-datadog/setup.cfg

@@ -38,7 +38,7 @@ package_dir=
     =src
 packages=find_namespace:
 install_requires =
-    ddtrace>=0.34.0
+    ddtrace>=0.34.0,<0.47.0
     opentelemetry-api == 1.0.0
     opentelemetry-sdk == 1.0.0