doc: fix incorrect method invocation on vm.Module instance

In the VM docs, under section `Constructor: new vm.Module`, the code
example incorrectly uses `module.initialize()`.

Change it to the correct method `module.instantiate()`.

Fixes: nodejs#21904

doc/api/vm.md

@@ -198,7 +198,7 @@ const contextifiedSandbox = vm.createContext({ secret: 42 });
     });
   // Since module has no dependencies, the linker function will never be called.
   await module.link(() => {});
-  module.initialize();
+  module.instantiate();
   await module.evaluate();
 
   // Now, Object.prototype.secret will be equal to 42.