Updates aws-xray-sdk to version 2.8.0 (DataDog#151)

Author: varunbhoopalam

setup.py

@@ -28,7 +28,7 @@
     packages=["datadog_lambda"],
     python_requires=">=2.7, !=3.0.*, !=3.1.*, !=3.2.*, !=3.3.*, !=3.4.*, !=3.5.*, <4",
     install_requires=[
-        "aws-xray-sdk==2.6.0",
+        "aws-xray-sdk==2.8.0",
         "datadog==0.41.0",
         "ddtrace==0.48.0",
         "wrapt==1.11.2",