add support for .NET CORE (#12)

* add support for .netcore on Imaging library

Author: fw2568

src/CloudInit.ConfigDrive.WindowsImaging/CloudInit.ConfigDrive.WindowsImaging.csproj

@@ -1,7 +1,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net45</TargetFramework>
+    <TargetFrameworks>net45;netcoreapp2.0</TargetFrameworks>
     <AssemblyName>Haipa.CloudInit.ConfigDrive.WindowsImaging</AssemblyName>
     <RootNamespace>Haipa.CloudInit.ConfigDrive</RootNamespace>
     <GeneratePackageOnBuild>true</GeneratePackageOnBuild>