Update `dispatch_async` to take a default `queue`

dispatch_async

import Dispatch

func dispatch_async(queue: dispatch_queue_t = dispatch_get_main_queue(), block: dispatch_block_t) {
    Dispatch.dispatch_async(queue, block)
}

dispatch_async {
    // Update the UI
}

// Alternatively, a less "hacky" solution

func async_main(block: dispatch_block_t) {
    dispatch_async(dispatch_get_main_queue(), block)
}

async_main {
    // Update the UI
}