olbrichj/promise-error.swift

## promise-error.swift
fetchPromise().then { value in
    return errorPromise(value) // this will throw an error
}.then { value in
    //this will not execute on error
}.catch { error in
    //we got an error
}
	fetchPromise().then { value in
	return errorPromise(value) // this will throw an error
	}.then { value in
	//this will not execute on error
	}.catch { error in
	//we got an error
	}