You have the answer on the following link https://answers.unrealengine.com/questions/25346/how-to-use-editor-classes-from-within-an-actor-cla.html.
Basically you have to add the UnrealEd module Into your Build.cs file. You have to have something like this:
PublicDependencyModuleNames.AddRange(new string[] { “Core”, “CoreUObject”, “Engine”, “InputCore”, “UnrealEd” });
And recompile your project again.