Fix enclosedSwiftAttributes in Swift 4.1

[marcelofabri]

Fixes #2019

key.attributes now contains key.offset and key.length, which are numbers.

[SwiftLintBot]

	12 Messages
📖	Linting Aerial with this PR took 0.44s vs 0.4s on master (9% slower)
📖	Linting Alamofire with this PR took 3.36s vs 3.3s on master (1% slower)
📖	Linting Firefox with this PR took 13.1s vs 12.98s on master (0% slower)
📖	Linting Kickstarter with this PR took 20.44s vs 20.61s on master (0% faster)
📖	Linting Moya with this PR took 1.83s vs 1.8s on master (1% slower)
📖	Linting Nimble with this PR took 1.94s vs 1.92s on master (1% slower)
📖	Linting Quick with this PR took 0.55s vs 0.57s on master (3% faster)
📖	Linting Realm with this PR took 3.62s vs 3.56s on master (1% slower)
📖	Linting SourceKitten with this PR took 1.1s vs 1.13s on master (2% faster)
📖	Linting Sourcery with this PR took 4.88s vs 5.03s on master (2% faster)
📖	Linting Swift with this PR took 13.81s vs 14.55s on master (5% faster)
📖	Linting WordPress with this PR took 14.93s vs 15.39s on master (2% faster)

Generated by 🚫 Danger

[codecov-io]

Codecov Report

Merging #2020 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #2020      +/-   ##
==========================================
+ Coverage   89.65%   89.66%   +<.01%     
==========================================
  Files         254      254              
  Lines       14862    14862              
  Branches      967      967              
==========================================
+ Hits        13325    13326       +1     
+ Misses       1519     1518       -1     
  Partials       18       18

Impacted Files	Coverage Δ
...intFramework/Extensions/Dictionary+SwiftLint.swift	85.71% <100%> (+0.14%)	⬆️
...SwiftLintFramework/Extensions/File+SwiftLint.swift	95.11% <0%> (+0.35%)	⬆️

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[Coeur]

Oh please release it soon. :)
I have to disable SwiftLint with Xcode 9.3 in the mean time.