Xcode 10.2 beta showing error for Image

[asomethings]

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Issue Description

The new release of Xcode (which is 10.2 Beta) is producing errors

What

Kingfisher/Sources/Image/Image.swift

Line 233 in 20d3f03

image?.kf.animatedImageData = data

Error showes up in above code. Saying Cannot mutate property 'kf' of immutable value 'image'.

Reproduce

Download Xcode 10.2 beta from apple developer site and build KingFisher. Done.

Other Comment

I'll make an PR for this

[onevcat]

There is already a PR #1098 for Swift 5 support. We are waiting for CI support for Xcode 10.2 before we can merge it into master. If you need Swift 5 for now, please use the "swift5.0" branch instead.