test: Remove support for Node 18 (#129)

Author: BilalQamar95

.github/workflows/ci.yml

@@ -11,14 +11,11 @@ on:
 jobs:
   tests:
     runs-on: ubuntu-latest
-    strategy:
-      matrix:
-        node: [18, 20]
 
     steps:
     - uses: actions/checkout@v3
     - uses: actions/setup-node@v4
       with:
-        node-version: ${{ env.NODE_VER }}
+        node-version-file: '.nvmrc'
     - run: npm ci
     - run: npm run lint