ci: Adjust build agents

.vsts-ci.yml

@@ -82,7 +82,7 @@ jobs:
     clean: all
 
   pool:
-    vmImage: 'ubuntu-20.04'
+    vmImage: 'ubuntu-latest'
     
   variables:
     NUGET_PACKAGES: $(Agent.WorkFolder)/.nuget
@@ -108,7 +108,7 @@ jobs:
 - job: macOS
 
   pool:
-    vmImage: 'macOS-10.15'
+    vmImage: 'macOS-latest'
 
   variables:
     NUGET_PACKAGES: $(Agent.WorkFolder)/.nuget