Reinstate NuGet publishing [Skip CI]

Author: nblumhardt

appveyor.yml

@@ -14,6 +14,12 @@ test: off
 artifacts:
 - path: artifacts/Serilog.*.nupkg
 deploy:
+- provider: NuGet
+  api_key:
+    secure: nvZ/z+pMS91b3kG4DgfES5AcmwwGoBYQxr9kp4XiJHj25SAlgdIxFx++1N0lFH2x
+  skip_symbols: true
+  on:
+    branch: /^(master|dev)$/
 - provider: GitHub
   auth_token:
     secure: p4LpVhBKxGS5WqucHxFQ5c7C8cP74kbNB0Z8k9Oxx/PMaDQ1+ibmoexNqVU5ZlmX