Fix: README.md ocmproviders.json example

The trailing comma is a syntax error,
the correct name is not providers.json, but ocmproviders.json

(The table in https://doc.owncloud.com/ocis/5.0/deployment/services/s-list/ocm.html#environment-variables
has the name spelled with a hyphen, this is misleading, as it is just a soft-hyphen due to the narrow column, and the hyphen disappears during copy/paste. )

services/ocm/README.md

@@ -19,7 +19,7 @@ The `ocm` services implements an invitation workflow which needs to be followed
 
 The list of trusted instances is managed by the `ocmproviderauthorizer` service. The only supported backend currently is `json` which stores the list in a json file on disk.
 
-Example `providers.json` file:
+Example `ocmproviders.json` file:
 ```
 [
     {
@@ -43,7 +43,7 @@ Example `providers.json` file:
                 "host": "example.com"
             }
         ]
-    },
+    }
 ]
 ```