Update EngineApiVersion.cs

Author: CharliePoole

src/NUnitEngine/EngineApiVersion.cs

@@ -5,4 +5,4 @@
 [assembly: AssemblyProduct("NUnit Engine API")]
 [assembly: AssemblyVersion("3.0.0.0")]
 [assembly: AssemblyInformationalVersion("4.0.0")]
-[assembly: AssemblyFileVersion("3.13.0")]
+[assembly: AssemblyFileVersion("4.0.0")]