consider making esri-loader a peer dependency

[tomwayson]

This might be needed for ajturner/hub-components-ember#1 but it is a good idea in general

[tomwayson]

So in ajturner/hub-components-ember#2 I established that this is not needed, but in that case the ember app and the components are using different versions of esri-loader, which could ultimately lead to bad things.