Remove encoding for application/json in response

Change-Id: I33c5118035bc69ed810e9498bf1aaf5f7488ef17
Closes-Bug: #1677446
diff --git a/api/gabbits/stacks.yaml b/api/gabbits/stacks.yaml
index 3028018..73c03c4 100644
--- a/api/gabbits/stacks.yaml
+++ b/api/gabbits/stacks.yaml
@@ -7,7 +7,7 @@
   GET: /stacks
   status: 200
   response_headers:
-    content-type: application/json; charset=UTF-8
+    content-type: application/json
 
 - name: create empty stack
   POST: /stacks