chore: upgrade to node 18 (#1061)

* chore: change `localhost` -> `127.0.0.1`

There is a change in how Node does DNS resolution in Node 18 vs
16 -- `localhost` resolves to `::1`, which is the equivalent of
`127.0.0.1` but in IPv6 instead of IPv4. The server however is
only listening on IPv4.
Reference:
https://github.com/nodejs/node/issues/40702#issuecomment-958143154

* refactor: change node version on CI from 16 to 18

.github/workflows/ci.yml

@@ -10,7 +10,7 @@ on:
 
 env:
   NWAKU_VERSION: "v0.13.0"
-  NODE_JS: "16"
+  NODE_JS: "18"
 
 jobs:
   check:

packages/tests/src/nwaku.ts

@@ -395,7 +395,7 @@ export class Nwaku {
   }
 
   get rpcUrl(): string {
-    return `http://localhost:${this.rpcPort}/`;
+    return `http://127.0.0.1:${this.rpcPort}/`;
   }
 
   private async rpcCall<T>(