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-Template:
Name: dash
URL: see above

twig-code for plugin template manager:

id: {{id}}
mvalue: {{attributes.mvalue}}
test-value: {{attributes.test-value}}
test-value: {{ attribute(attributes, 'test-value') }}

Shortcode:

[jsoncontentimporterpro nameoftemplate="dash"]

In Action:

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