message: fix formatting for request example
diff: @@ -1190,13 +1190,16 @@ Additionally, applying this extension to a schema forces the schema to become a
  ```json
  "parameters": [
  + {
  "x-ms-meta": {
  "type": "string",
  "x-ms-client-name": "Metadata",
  "x-ms-header-collection-prefix": "x-ms-meta-"
  }
  + }
  ]
  ```
  +
  This request parameter will be forced to be a dictionary schema, and all keys in this dictionary will be prefixed with `x-ms-meta-`.
  So, if you input `{"key": "value"}` through this parameter, `{"x-ms-meta-key": "value"}` is what reaches the service.
  