chore: drop unsupported node versions on macOS

No change to logic. This drops support for older NodeJS versions on macOS
because GitHub Actions no longer supports them.

This also updates NodeJS to the latest LTS release.

Author: nfischer

.github/workflows/main.yml

@@ -17,10 +17,23 @@ jobs:
           - 14
           - 16
           - 18
+          - 20
+          - 22
         os:
           - ubuntu-latest
           - macos-latest
           - windows-latest
+        exclude:
+          - node-version: 6
+            os: macos-latest
+          - node-version: 8
+            os: macos-latest
+          - node-version: 10
+            os: macos-latest
+          - node-version: 12
+            os: macos-latest
+          - node-version: 14
+            os: macos-latest
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v2