Update README.md.

Author: qimingyuan

README.md

@@ -1,14 +1,14 @@
 # Dropbox.NET
 
-A .NET SDK for integrating with the Dropbox API v2 (preview version).
+A .NET SDK for integrating with the Dropbox API v2.
 
 ## Setup
 
 To get started with Dropbox.NET, we recommend you add it to your project using NuGet.
 
 To install `Dropbox.Api`, run the following command in the Package Manager Console:
 
-```PM> Install-Package Dropbox.Api -Pre```
+```PM> Install-Package Dropbox.Api```
 
 ## Creating an application