fix appveyor.yml

Author: seayxu

GodSharp.SerialPort.sln

@@ -1,7 +1,7 @@
 
 Microsoft Visual Studio Solution File, Format Version 12.00
 # Visual Studio 15
-VisualStudioVersion = 15.0.26403.0
+VisualStudioVersion = 15.0.26403.3
 MinimumVisualStudioVersion = 10.0.40219.1
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "src", "src", "{A9C28F7F-0F11-4E92-B31A-BF950A54F863}"
 EndProject
@@ -18,6 +18,7 @@ EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution Items", "{29956551-411E-4631-A3E3-397100FCD8B8}"
 	ProjectSection(SolutionItems) = preProject
 		.gitignore = .gitignore
+		appveyor.yml = appveyor.yml
 		LICENSE = LICENSE
 		README.md = README.md
 	EndProjectSection

appveyor.yml

@@ -6,6 +6,8 @@ image: Visual Studio 2017
 configuration: Release
 platform: Any CPU
 clone_folder: c:\projects\godsharp.serialport
+init:
+- cmd: nuget restore
 nuget:
   account_feed: true
   project_feed: true