writeout_json: add missing comma to fix the HTTP version

Follow-up to 04c03416e68fd635a15
diff --git a/src/tool_writeout_json.c b/src/tool_writeout_json.c
index 99252ec..703cbbd 100644
--- a/src/tool_writeout_json.c
+++ b/src/tool_writeout_json.c
@@ -34,7 +34,7 @@
   "0",   /* CURL_HTTP_VERSION_NONE */
   "1",   /* CURL_HTTP_VERSION_1_0 */
   "1.1", /* CURL_HTTP_VERSION_1_1 */
-  "2"    /* CURL_HTTP_VERSION_2 */
+  "2",   /* CURL_HTTP_VERSION_2 */
   "3"    /* CURL_HTTP_VERSION_3 */
 };