remove public trait from ImpressionData

Author: roninopf

iterableapi/src/main/java/com/iterable/iterableapi/ImpressionData.java

@@ -5,7 +5,7 @@
 import java.util.Date;
 
 @RestrictTo(RestrictTo.Scope.LIBRARY_GROUP)
-public class ImpressionData {
+class ImpressionData {
     final String messageId;
     final boolean silentInbox;
     int displayCount = 0;