Throws when used with ember-cli-babel `includeExternalHelpers: true`

[makepanic]

Hi,

when using ember-cli-flash in a project that enables includeExternalHelpers in its ember-cli-babel settings, the transpiled code will throw.

This happens because the addon/flash/object defines a Object class. During the transpilation babel adds the esModule marker:

Object.defineProperty(_exports, "__esModule", {
    value: true
});

// ...

var Object = (_dec = (0, _computed.guidFor)('message').readOnly(), (_class = (_temp = /*#__PURE__*/function (_Ember$Object$extend) {

Due to variable hoisting, it'll try to call defineProperty on the class that ember-cli-flash defined.

If it's ok, I'll open a PR to rename that class name to something like FlashObject which prevents this from happening.