Fix incorrect attribute name

The ChangeKind attribute exposed in the JSON was incorrectly written
originally.  The correct attribute in the JSON is "kind".

Change-Id: I225bb4cdb486810d8f8c3a3c9969a13ce70a0365
diff --git a/Documentation/json.txt b/Documentation/json.txt
index 6ab35f9..3624b3f 100644
--- a/Documentation/json.txt
+++ b/Documentation/json.txt
@@ -115,7 +115,7 @@
 
 isDraft:: Whether or not the patch set is a draft patch set.
 
-changeKind:: Kind of change uploaded.
+kind:: Kind of change uploaded.
 
   REWORK;; Nontrivial content changes.