Update actions/download-artifact action to v2

Author: renovate-bot

.github/workflows/build.yml

@@ -66,7 +66,7 @@ jobs:
     runs-on: windows-latest
     steps:
       - name: 'Download Artefact'
-        uses: actions/download-artifact@v1
+        uses: actions/download-artifact@v2
         with:
           name: 'windows-latest'
       - name: 'Dotnet NuGet Add Source'
@@ -86,7 +86,7 @@ jobs:
     runs-on: windows-latest
     steps:
       - name: 'Download Artefact'
-        uses: actions/download-artifact@v1
+        uses: actions/download-artifact@v2
         with:
           name: 'windows-latest'
       - name: 'Dotnet NuGet Push'