Merge pull request #30 from sophia-guo/ubuntulatest

Update ubuntu to latest as 16 is depreciated

Author: Shelley Lambert

.github/workflows/nightly.yml

@@ -30,7 +30,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        os: [ubuntu-16.04, macos-10.15, windows-2016]
+        os: [ubuntu-latest, macos-10.15, windows-2016]
         version: [8, 11, 16]
         exclude:
         # excludes jdk 8 on Mac( not valid), jdk8 on windows( not enabled), jdk11 on windows( issue opened)