Migrating to Swift 4.2/Xcode 10

[RomanPodymov]

Good evening.
Thank you for this library, it looks very interesting.
I'd like to add support of Swift 4.2 for the localizenib-ios and here is what I did:

• Set Swift version to 4.2;
• Added Gemfile for easier installation of dependencies written in Ruby;
• Clean code with swiftlint autocorrect;
• Declared "!!!" as a computable property;
• Fixed all warnings.

[jankaltoun]

Hi Roman, thank you for your contribution!

@dzindra please take a look.

[dzindra]

Hi Roman, thanks for your pull request. I checked it and commented on some changes you made. Also when I try to compile code, it fails on UIControlState type changed in Swift 4.2. Please address the issues and I will merge your PR.

https://github.com/RomanPodymov/localizenib-ios/blob/d3e4a12133e713d97fc41792935249987dbb53de/LocalizeNIB/LocalizeNIB.swift#L172