[bug?] Nested machines immediate issue

[kybarg]

When using invoke to run nested machines current doenst't represent deepest child

Here is example
https://codesandbox.io/s/react-robot-bug-example-re781

robot/machine.js

Lines 174 to 181 in 31d8125

	let service = {
	send(event) {
	this.machine = send(this, event);
	// TODO detect change
	this.onChange(this);
	}
	};

this quick fix helped, but this looks wrong😁

let service = {
  send(event) {
    this.machine = send(this, event);

    // TODO detect change
-    this.onChange(this);
+    this.onChange(this.child || this)
  }
};

[afn]

This appears to remain an issue in the latest version (0.4.0).