Add session token in README.md

Author: caowei-amazon

README.md

@@ -324,8 +324,8 @@ We have 2 different types of tests:
 	```sh
 	export AWS_ACCESS_KEY_ID=YOUR_ACCESS_KEY_ID
 	export AWS_SECRET_ACCESS_KEY=YOUR_ACCESS_KEY
+	export AWS_SESSION_TOKEN=YOUR_AWS_SESSION_TOKEN
 	export AWS_REGION=us-west-2
- 	export AWS_SESSION_TOKEN=Your_AWS_SESSION_TOKEN
 	./gradlew integ
 	```