Fix json view files

``` ruby
#<ActionDispatch::Request:0x00000004aae160
@env={"REMOTE_ADDR"=>"127.0.0.1", "REQUEST_METHOD"=>"GET", "REQUEST_PATH"=>"/project_path_with_namespace/tree/master/full/path/to/file.json", "PATH_INFO"=>"/project_path_with_namespace">
@request_method="GET",
@filtered_parameters={"action"=>"show", "controller"=>"tree", "project_id"=>"project_path_with_namespace", "id"=>"master/full/path/to/file.json"},
@method="GET",
@fullpath="/project_path_with_namespace/tree/master/full/path/to/file.json">
```

Correctly extract refs from `id`. Rails can parse request better than we do it.

Related #3330