Replace the last loadimpact.com test domains with k6.io

part of grafana/k6#1400

Author: mstoykov

src/data/markdown/docs/02 javascript api/06 k6-http/61 Response/Response-json- -selector- -.md

@@ -25,7 +25,7 @@ This method takes an object argument where the following properties can be set:
 import http from 'k6/http';
 
 export default function () {
-  let res = http.get('https://test-api.loadimpact.com/public/crocodiles/');
+  let res = http.get('https://test-api.k6.io/public/crocodiles/')
 
   console.log(res.json());
 }

src/data/markdown/docs/06 Cloud REST API/01 Cloud REST API/06 Test Run Metrics.md

@@ -91,13 +91,13 @@ Returns details of a metric with the specified ID.
   },
   "k6-group": {
     "id": "223813452fd767e624ba9ee6c78bde91",
-    "name": "page_1 - http://test.loadimpact.com/"
+    "name": "page_1 - http://test.k6.io/"
   },
   "k6-url": {
     "id": "81414ab976a1985f59b321d6b745d2c2",
     "method": "GET",
     "status": 200,
-    "url": "http://test.loadimpact.com/"
+    "url": "http://test.k6.io/"
   }
 }
 ```