Updating key for android push image.

Author: davidtruong

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

@@ -55,7 +55,7 @@ public final class IterableConstants {
     public static final String IS_GHOST_PUSH        = "isGhostPush";
     public static final String ITERABLE_DATA_BODY   = "body";
     public static final String ITERABLE_DATA_KEY    = "itbl";
-    public static final String ITERABLE_DATA_PUSH_IMAGE  = "pushImage";
+    public static final String ITERABLE_DATA_PUSH_IMAGE  = "attachment_url";
     public static final String ITERABLE_DATA_SOUND  = "sound";
     public static final String ITERABLE_DATA_TITLE  = "title";