Update to NuGet 5.3.1 and configure feeds

The default tool was even older than 4.4.1. For some reason, Azure
Pipelines defaulted to changing the NuGet packages configuration even
though the repository contains a NuGet.config. Update the NuGetCommand
task to not use the invalid defaults it provided.

Author: sharwell

azure-pipelines.yml

@@ -18,10 +18,17 @@ jobs:
       Release:
         BuildConfiguration: Release
   steps:
+  - task: NuGetToolInstaller@0
+    displayName: 'Use NuGet 5.3.1'
+    inputs:
+      versionSpec: 5.3.1
+
   - task: NuGetCommand@2
     displayName: 'NuGet restore'
     inputs:
       restoreSolution: '$(BuildSolution)'
+      feedsToUse: 'config'
+      nugetConfigPath: '$(Build.WorkingDirectory)/NuGet.config'
 
   - task: VSBuild@1
     displayName: 'Build solution StyleCopAnalyzers.sln'