Test runner: update node version and add back ubuntu-latest

Author: darkriszty

.github/workflows/test.yml

@@ -12,8 +12,8 @@ jobs:
 
     strategy:
       matrix:
-        os: [ macos-latest, windows-latest ]
-        node-version: [ '12.x', '14.x', '15.x' ]
+        os: [ ubuntu-latest, macos-latest, windows-latest ]
+        node-version: [ '14.x', '16.x' ]
 
     steps:
     - uses: actions/checkout@v2