make didShake function run in UI threand

[makhocheung]

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[ezefranca]

Thank you @makhocheung

[makhocheung]

I forgot an another problem. I issue it here.
WatchShaker is not an ObservableObject currently, so I need extend it like this in my SwiftUI project to use shake publisher.

extension WatchShaker: ObservableObject {
    
}

I think it is better that WatchShaker can implement ObservableObject protocol. But this is not a big problem.