Bump Ubuntu runner to 20.04

Author: sergiou87

.github/workflows/ci.yml

@@ -20,9 +20,9 @@ jobs:
     strategy:
       matrix:
         node-version: [15.x]
-        os: [ubuntu-16.04, windows-latest, macos-latest]
+        os: [ubuntu-20.04, windows-latest, macos-latest]
         include:
-          - os: ubuntu-16.04
+          - os: ubuntu-20.04
             friendlyName: Ubuntu
           - os: windows-latest
             friendlyName: Windows