Set interface with prerel tag for preview (#503)

* Set interface with prerel tag for preview

* fix build badge

Author: Oren Novotny

README.md

@@ -3,7 +3,7 @@ Reactive Extensions
 
 Channel  | Rx | Ix |
 -------- | :------------: | :-------------: |
-AppVeyor<br>([home](https://ci.appveyor.com/project/dotnetfoundation/rx-net)) | ![#](https://img.shields.io/appveyor/ci/dotnetfoundation/rx-net/master.svg) | ![#](https://img.shields.io/appveyor/ci/dotnetfoundation/rx-net/master.svg)
+VSTS | ![#](https://dotnetfoundation.visualstudio.com/_apis/public/build/definitions/ba70dafd-6b93-4176-b27f-975148db36bd/9/badge) | 
 NuGet.org | [![#](https://img.shields.io/nuget/v/System.Reactive.svg)](https://www.nuget.org/packages/System.Reactive/) | [![#](https://img.shields.io/nuget/v/System.Interactive.svg)](https://www.nuget.org/packages/System.Interactive/)
 MyGet<br>([gallery](https://dotnet.myget.org/gallery/rx)) | ![#](https://img.shields.io/dotnet.myget/rx/vpre/System.Reactive.svg)<br>![#](https://img.shields.io/dotnet.myget/rx/v/System.Reactive.svg) | ![#](https://img.shields.io/dotnet.myget/rx/vpre/System.Interactive.svg)<br>![#](https://img.shields.io/dotnet.myget/rx/v/System.Interactive.svg)  
 

Rx.NET/Source/System.Reactive.sln

@@ -18,8 +18,10 @@ Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Solution Items", "Solution
 		build-new.ps1 = build-new.ps1
 		Directory.build.props = Directory.build.props
 		Directory.build.targets = Directory.build.targets
+		global.json = global.json
 		Rx.ruleset = Rx.ruleset
 		Test.ruleset = Test.ruleset
+		version.json = version.json
 	EndProjectSection
 EndProject
 Project("{2150E333-8FDC-42A3-9474-1A3956D46DE8}") = "Tests", "Tests", "{D324579D-CBE6-4867-8980-D7842C7C45A2}"
@@ -325,4 +327,7 @@ Global
 		{4DCC120A-FD19-409B-A0E6-A049C4D0B663} = {A0F39260-B8F8-4FCB-9679-0ED917A22BDF}
 		{E9BB350B-D4EF-42E1-B4E2-14058AC6809B} = {A0F39260-B8F8-4FCB-9679-0ED917A22BDF}
 	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {A71771B3-8AA0-43A5-988A-9C86D422B7CD}
+	EndGlobalSection
 EndGlobal

Rx.NET/Source/src/System.Reactive.Interfaces/version.json

@@ -1,4 +1,4 @@
 {
-  "version": "4.0.0",
+  "version": "4.0.0-preview.2.build.{height}",
   "inherit": true
 }