Kingfisher: Swift 4.1 and Xcode 9.3 deprecations

[maziyarpanahi]

Hi
After updating Xcode 9.3 which is shipped with Swift 4.1, there are two deprecations here:

swift valuePointer.deinitialize() // 'deinitialize()' is deprecated: the default argument to deinitialize(count:) has been removed, please specify the count explicitly valuePointer.deallocate(capacity: 1) // 'deallocate(capacity:)' is deprecated: Swift currently only supports freeing entire heap blocks, use deallocate() instead

https://swift.org/blog/swift-4-1-released/

[onevcat]

Should be fixed in #889