Handle `CallExpression` for debug macros.

Currently, we are handling only `ExpressionStatement`'s for debug macro replacement. Unfortunately, the following do not get processed (since they do not include an `ExpressionStatement`):

```js
function foo() {
return assert(false, 'derp'); // ReturnStatement
}

let qux = () => assert(false, 'herp'); // ArrowFunctionExpression
```

This is the underlying issue in https://github.com/babel/ember-cli-babel/issues/168.