tslib dependency should not be in devDependencies

[Jacob Thomas Errington]

When installing production-only dependencies for our app, we use npm install --production, which does not install devDependencies neither for our app or any of our app's dependencies such as itiriri-async. But the thing is, itiriri-async lists tslib as a devDependency. tslib is the typescript runtime, so it should be a production dependency. In fact, our app fails to run unless we install tslib separately ourselves becausee of this.