twig: Handle dash in JSON

If JSON contains some dashes (“-“) in the keys, the usual way of twig does not work. Here you finde how to solve this: JSON: http://api.json-content-importer.com/extra/json/dash.json
{"id":"327456",
"attributes":
{"test-value":"2352.07597459064", 
"mvalue":"543543.067567575"}
}

twig-code for plugin template manager:
id: {{id}}
mvalue: {{attributes.mvalue}}
test-value: {{attributes.test-value}}
test-value: {{ attribute(attributes, 'test-value') }}

Shortcode:
[jsoncontentimporterpro url=http://api.json-content-importer.com/extra/json/dash.json id=ID_TEMPLATE_MANAGER]

In Action:
id: 327456
mvalue: 543543.067567575
test-value: 0
test-value: 2352.07597459064