ci(azure-pipelines.yml): change the Ubuntu VM to 'latest' (#860)

* Changes Ubuntu VM to no longer point to deprecated VM
(https://github.com/actions/virtual-environments/tree/df27520b1f223f23188191ec1a3fdce76f5cddd8#available-environments)

Author: dmwelch

azure-pipelines.yml

@@ -14,7 +14,7 @@ jobs:
   parameters:
     name: Linux
     pool:
-      vmImage: 'Ubuntu-16.04'
+      vmImage: 'ubuntu-latest'
 
 - template: jobs/build.yml  # Template reference
   parameters: