Run GHA tests against Node 18 for CI

Author: pimterry

.github/workflows/ci.yml

@@ -7,7 +7,7 @@ jobs:
 
     strategy:
       matrix:
-        node-version: [14.x, v14.18.3, 16.x, '*']
+        node-version: [14.x, v14.18.3, 16.x, 18.x, '*']
 
     steps:
       - uses: actions/checkout@v2