Update README.md (#224)

Author: sergiobelya

README.md

@@ -63,7 +63,7 @@ Option | Description
 `router` | The router to use, when processing the route files (can be Laravel or Dingo - defaults to Laravel)
 `bindings` | List of route bindings that should be replaced when trying to retrieve route results. Syntax format: `binding_one,id|binding_two,id`
 `force` | Force the re-generation of existing/modified API routes
-`header` | Custom HTTP headers to add to the example requests. Separate the header name and value with ":". For example: `--header 'Authorization: CustomToken'`
+`header` | Custom HTTP headers to add to the example requests. Separate the header name and value with ":". For example: `--header="Authorization: CustomToken"`
 
 ## Publish rule descriptions for customisation or translation.