Swift version fixes

[RomanPodymov]

Hello.
Thank you for Fashion.
In this pull request I deleted deprecated .swift-version file and set Swift version with s.swift_versions.
Probably fixed #18.

[vadymmarkov]

Thanks @RomanPodymov

[larsriehn]

@vadymmarkov Thank you for looking at my request. Unfortunately it does not fix my problem.
Roman did change something but not in the file I mentioned and I think this still is the problem.
When I look in Fashion.debug.podspecc (or Fashion.release.podspecc) I see this line:
SWIFT_VERSION = 3.0
When I look in *.podspec files of other pod's they do not have this line at all.

[RomanPodymov]

Hello @larsriehn
In #18 you mentioned https://github.com/CocoaPods/Specs/blob/master/Specs/9/3/e/Fashion/4.0.0/Fashion.podspec.json. But now the latest Fashion version is 4.2.0 and in https://github.com/CocoaPods/Specs/blob/master/Specs/9/3/e/Fashion/4.2.0/Fashion.podspec.json "swift_version" is "5.0". Could you please provide us a small project where we can reproduce your issue?