Merge pull request #53 from JohanMabille/ci

Migrated to Ubuntu 18.04 on Azure ci

Author: JohanMabille

.azure-pipelines/azure-pipelines-linux.yml

@@ -3,7 +3,7 @@ jobs:
     strategy:
       matrix:
         gcc_7:
-          image_name: 'ubuntu-16.04'
+          image_name: 'ubuntu-18.04'
     pool:
       vmImage: $(image_name)
     timeoutInMinutes: 360