build: include Babel polyfill

[buschtoens]

Resolves IE freezing mentioned in #67

[alexander-alvarez]

relates to #51 no?

[buschtoens]

Not really. The ember-cli-build.js file only affects the build of the addon dummy app.

We could force the polyfill inclusion via the included hook, but I consider that bad practice. We should probably add a note to the readme though.

[alexander-alvarez]

i'm pretty sure #50 is the only non IE. functionality in ember-scrollable, do you think there's something else that requires the pollyfills for compatibility?

[buschtoens]

I believe it's the only thing. In my case it doesn't really matter as we include the polyfill anyways, as we use other ES6 features in our app as well. The polyfill and regenerator runtime add about 28 k gzipped, possibly less.

I can understand that some folks would not want to add this (arguably small) added weight for an addon that could easily avoid this.

While I'd rather stay true to ES6 all the way, I have no objections against including the inline safety net (#50 (comment)) or a one line polyfill.

[buschtoens]

Superseded by #69.