Update demos to Swift 4

[jeffmcnd]

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I came to this repo to help an iOS developer with barcode detections only to come across these demos written in Objective-C. This is a blast from the past and these demos should be updated to Swift (preferably 4). I don't know Swift myself, but would greatly appreciate it if someone could update this repo.

[ducpt2]

+1. I try to follow document Google Mobile vision (barcode detect) with Swift, can not work at all. Using pod install, the command install all different library (compare with this sample) and complie always throw error. Please create a Swift example and make a better document then developer can use it. Thanks.

[zhaoyuhang]

I am trying to use these objective-c codes in my swift projects. Maybe it's a good way now