fix: add support for classes with decorators

[homer0]

What does this PR do?

When using decorators with Babel, Babel creates a sequence wrapper in order to apply the decorators, something like this:

let Hello = (_class = (_temp = (_temp2 = class Hello {
  constructor(someService) {
    'inject';

    _initializerDefineProperty(this, "random", _descriptor, this);
  }
}, _temp2), _temp), (_descriptor = _applyDecoratedDescriptor(_class.prototype, "random", [aurelia_framework__WEBPACK_IMPORTED_MODULE_0__["bindable"]], {
  configurable: true,
  enumerable: true,
  writable: true,
  initializer: function () {
    return 'something';
  }
})), _class);

And when this plugin tries to add the inject property, it ends up between the class expression and _temp2, making the code invalid and breaking the execution.

The solution I implemented here is that, when working with a class, if the class is inside a sequence expression, the plugin will crawl all the way up until the top path is the program itself, and then add the definition:

})), _class);
+ Hello.inject = ['something'];

Yes, I'm not good at working with Babel ASTs :P.

How should it be tested manually?

1. Try using the current release on a class with a decorator, it should break.
2. Use this branch and everything should go back like it was before.

[coveralls]

Coverage remained the same at 100.0% when pulling fa84f6e on homer0_decoratorsFix into 1c1e1c8 on master.