Changed body to lowercase. (#236)

Author: msailes

aws-lambda-java-events/src/main/java/com/amazonaws/services/lambda/runtime/events/APIGatewayV2HTTPEvent.java

@@ -38,7 +38,7 @@ public class APIGatewayV2HTTPEvent {
     private Map<String, String> queryStringParameters;
     private Map<String, String> pathParameters;
     private Map<String, String> stageVariables;
-    private String Body;
+    private String body;
     private boolean isBase64Encoded;
     private RequestContext requestContext;