Add Node 18 to CI instead of 17

17 is an unstable version, so now that 18 is out for while,
update the tests to add Node 18 in place of Node 17

Signed-off-by: Daniel F. Dickinson <dfdpublic@wildtechgarden.ca>

.github/workflows/ci.yml

@@ -18,7 +18,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        node-version: ['16', '17']
+        node-version: ['16', '18']
     steps:
     - uses: actions/checkout@v3
     - name: Use Node.js ${{ matrix.node-version }}