Bum version to 4.0.0-preview

Author: ravazquez

deployment/main.VL.OpenCV.nuspec

@@ -2,7 +2,7 @@
 <package xmlns="http://schemas.microsoft.com/packaging/2011/10/nuspec.xsd">
   <metadata>
     <id>VL.OpenCV</id>
-    <version>3.1.0-preview</version>
+    <version>4.0.0-preview</version>
     <title>VL.OpenCV</title>
     <authors>Randall Vásquez, vvvv</authors>
     <owners>vvvv</owners>