test: bump CircleCI node to v18.18

- It seems CircleCI has not been working since a while ago, because some
  dependencies require a newer Node than v8.x. Bumps the Node version to
  the current LTS version v18.18. However, this may break existing
  tests.

.circleci/config.yml

@@ -4,7 +4,7 @@ jobs:
     working_directory: ~/repo
     docker:
       # specify the version you desire here
-      - image: circleci/node:8.10-browsers
+      - image: cimg/node:18.18-browsers
     steps:
       # Checkout repository
       - checkout