Warn lors de l'import d'un JSON dans des projets JS

Je l'avais remonté à @tsecher sur son ancien repo, mais la méthode proposée sur le readme génère des warns car `assert {type: 'json'}` pourrait être abandonné par Node à tout moment.

```shell
(node:1884) ExperimentalWarning: Importing JSON modules is an experimental feature and might change at any time
```

Il faudrait proposer, en plus de ce JSON un JS qui ferait exactement la même chose et l'ajouter dans les files du `package.json`.

```javascript
// ecoindex_reference.js
module.exports = {
"quantiles": {
"dom_size": [
0,
47,
75,
159,
233,
298,
358,
417,
476,
537,
603,
674,
753,
843,
949,
1076,
1237,
1459,
1801,
2479,
594601
],
"nb_request": [
0,
2,
15,
25,
34,
42,
49,
56,
63,
70,
78,
86,
95,
105,
117,
130,
147,
170,
205,
281,
3920
],
"response_size": [
0,
1.37,
144.7,
319.53,
479.46,
631.97,
783.38,
937.91,
1098.62,
1265.47,
1448.32,
1648.27,
1876.08,
2142.06,
2465.37,
2866.31,
3401.59,
4155.73,
5400.08,
8037.54,
223212.26
]
},
"targets": {
"dom_size": 600,
"nb_request": 40,
"response_size": 1024
},
"medians": {
"dom_size": 693,
"nb_request": 78,
"response_size": 2420
},
"grades": [
{
"value": 80,
"grade": "A",
"color": "#349A47"
},
{
"value": 70,
"grade": "B",
"color": "#51B84B"
},
{
"value": 55,
"grade": "C",
"color": "#CADB2A"
},
{
"value": 40,
"grade": "D",
"color": "#F6EB15"
},
{
"value": 25,
"grade": "E",
"color": "#FECD06"
},
{
"value": 10,
"grade": "F",
"color": "#F99839"
},
{
"value": 0,
"grade": "G",
"color": "#ED2124"
}
]
}
```