Fix mqtt version

Author: pirropirro

package.json

@@ -17,7 +17,7 @@
   "dependencies": {
     "@arduino/cbor-js": "arduino/cbor-js",
     "jws": "^4.0.0",
-    "mqtt": "^4.1.0",
+    "mqtt": "4.1.0",
     "node-fetch": "^2.6.0",
     "rxjs": "^6.5.5",
     "whatwg-fetch": "^3.0.0"