Remove trailing comma from last config line

The settings.json.template file has a trailing comma in it. This is likely because it shows an example configuration after this line, but this line is the last one that will be interpreted by the program in default configuration, so the comma should be removed.

settings.json.template

@@ -28,7 +28,7 @@
   */
 
   /* The default selected tool - 'pencil', 'brush', 'select' */
-  "tool": "brush",
+  "tool": "brush"
 
   /* Example SSL Configuration
     "ssl" : {