Add explicit windowsbase reference (#509)

* add explicit windowsbase reference

* set to preview 3

* Update version.json

Rx.NET/Source/src/System.Reactive/System.Reactive.csproj

@@ -51,6 +51,7 @@
   <ItemGroup Condition=" '$(TargetFramework)' == 'net45' or '$(TargetFramework)' == 'net46'">
     <Reference Include="System.Windows" />
     <Reference Include="System.Windows.Forms" />
+    <Reference Include="WindowsBase" />
     <Compile Include="Platforms\Desktop\**\*.cs" />
   </ItemGroup>
   

Rx.NET/Source/version.json

@@ -1,8 +1,8 @@
 {
-  "version": "4.0.0-preview.2.build.{height}",
+  "version": "4.0.0-preview.3.build.{height}",
   "publicReleaseRefSpec": [
     "^refs/heads/master$", // we release out of master
-    "^refs/heads/develop$", // we release out of develop
+    "^refs/heads/rel/v\\d+\\.\\d+", // we also release tags starting with vN.N
     "^refs/tags/v\\d+\\.\\d+" // we also release tags starting with vN.N
   ],
   "nugetPackageVersion":{