Add missing comma to example JSON

docs/communities.md

@@ -197,7 +197,7 @@ The standard format for `custom_json` ops:
 ["setRole", {
     "community": <community>,
     "account": <account>,
-    "role": admin|mod|member|none|muted
+    "role": admin|mod|member|none|muted,
     "notes": <comment>
 }]
 ```
@@ -444,4 +444,4 @@ modlog
 
 1. Stratos subapp: Communities
 
-   https://github.com/stratos-steem/stratos/wiki/Subapp:-Communities
\ No newline at end of file
+   https://github.com/stratos-steem/stratos/wiki/Subapp:-Communities