Remove Swift 4.0 from supported versions
Remove Swift 4.0 from supported versions

https://bugs.swift.org/browse/SR-2 was resolved in Swift 4.1. In order
to fix #345, we need to remove support for Swift 4.0.

We could add support for Swift 4.1, but I believe it’s better to
increase the minimum version directly to Swift 4.2 because BonMot
already officially supports and runs CI on Swift 4.2.

Raizlabs/BonMot,Raizlabs/BonMot,Raizlabs/BonMot