config: Remove trailing comma in CAP_KILL examples

Fix a JSON typo which snuck in with eb114f0 (Add ambient and bounding
capability support, 2017-02-02, opencontainers#675).

Signed-off-by: W. Trevor King <wking@tremily.us>

config.md

@@ -215,7 +215,7 @@ _Note: symbolic name for uid and gid, such as uname and gname respectively, are
         ],
         "effective": [
             "CAP_AUDIT_WRITE",
-            "CAP_KILL",
+            "CAP_KILL"
         ],
         "ambient": [
             "CAP_NET_BIND_SERVICE"
@@ -484,7 +484,7 @@ Here is a full example `config.json` for reference.
             ],
             "effective": [
                 "CAP_AUDIT_WRITE",
-                "CAP_KILL",
+                "CAP_KILL"
             ],
             "ambient": [
                 "CAP_NET_BIND_SERVICE"