Fixes the Yogakit compilation bug for xcode11

Summary:
This fixes the yogakit compilation bug for xcode 11, where it fails to find swift core frameworks for pure objc project.

https://github.com/Carthage/Carthage/issues/2825
https://twitter.com/krzyzanowskim/status/1151549874653081601?s=21

Also published this podspec on cocoapods and deleted .swift-version file as it was not required, because swift version is mentioned in podspec

Reviewed By: SidharthGuglani

Differential Revision: D18420963

fbshipit-source-id: d617bf643ac6481d6add86e6a4bfadd6e0d0c229

.swift-version

@@ -1 +0,0 @@
-4.0

YogaKit.podspec

@@ -5,7 +5,7 @@
 
 podspec = Pod::Spec.new do |spec|
   spec.name = 'YogaKit'
-  spec.version = '1.17.0'
+  spec.version = '1.18.1'
   spec.license =  { :type => 'MIT', :file => "LICENSE" }
   spec.homepage = 'https://facebook.github.io/yoga/'
   spec.documentation_url = 'https://facebook.github.io/yoga/docs/'
@@ -16,26 +16,22 @@ podspec = Pod::Spec.new do |spec|
   spec.authors = 'Facebook'
   spec.source = {
     :git => 'https://github.com/facebook/yoga.git',
-    :tag => spec.version.to_s,
+    :tag => "1.18.0",
   }
 
   spec.platform = :ios
   spec.ios.deployment_target = '8.0'
   spec.ios.frameworks = 'UIKit'
-  spec.default_subspec = "Core"
-  spec.dependency 'Yoga', '~> 1.14'
   spec.module_name = 'YogaKit'
-
-  spec.subspec "Core" do |ss|
-    ss.source_files = 'YogaKit/Source/*.{h,m}'
-    ss.public_header_files = 'YogaKit/Source/{YGLayout,UIView+Yoga}.h'
-    ss.private_header_files = 'YogaKit/Source/YGLayout+Private.h'
-  end
-
-  spec.subspec 'SwiftExtension' do |ss|
-    ss.source_files = 'YogaKit/Source/*.{swift}'
-  end
-
+  spec.dependency 'Yoga', '~> 1.14'
+  # Fixes the bug related the xcode 11 not able to find swift related frameworks.
+  # https://github.com/Carthage/Carthage/issues/2825
+  # https://twitter.com/krzyzanowskim/status/1151549874653081601?s=21
+  spec.pod_target_xcconfig = {"LD_VERIFY_BITCODE": "NO"}
+  spec.source_files = 'YogaKit/Source/*.{h,m,swift}'
+  spec.public_header_files = 'YogaKit/Source/{YGLayout,UIView+Yoga}.h'
+  spec.private_header_files = 'YogaKit/Source/YGLayout+Private.h'
+  spec.swift_version = '5.1'
 end
 
 # See https://github.com/facebook/yoga/pull/366