CI: revert back to 16.04 ubuntu

tacaswell · tacaswell · commit af966f4b1506 · 2020-02-29T18:22:53.000-05:00
We need to fix account for the changes to latex before we can bump this.
diff --git a/azure-pipelines.yml b/azure-pipelines.yml
@@ -12,7 +12,7 @@ strategy:
       vmImage: 'ubuntu-16.04'
       python.version: '3.7'
     Linux_py38:
-      vmImage: 'ubuntu-18.04'
+      vmImage: 'ubuntu-16.04'
       python.version: '3.8'
     macOS_py36:
       vmImage: 'macOS-10.14'
