chore: test on node 18 (#509)

Author: SimenB

.github/workflows/nodejs.yml

@@ -16,7 +16,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        node-version: [10.x, 12.x, 14.x, 16.x, 17.x]
+        node-version: [10.x, 12.x, 14.x, 16.x, 17.x, 18.x]
         os: [ubuntu-latest, windows-latest, macOS-latest]
 
     runs-on: ${{ matrix.os }}