[Travis] Explicit swift versions

Author: Hugo Tunius

.travis.yml

@@ -6,9 +6,13 @@ script:
 matrix:
   include:
     - osx_image: xcode10
-      env: BUILD_SDK=iphonesimulator12.0 DESTINATION="platform=iOS Simulator,name=iPhone 8"
+      env: SWIFT=4.2 BUILD_SDK=iphonesimulator12.0 DESTINATION="platform=iOS Simulator,name=iPhone 8"
+    - osx_image: xcode9.2
+      env: SWIFT=4.0 BUILD_SDK=iphonesimulator11.2 DESTINATION="platform=iOS Simulator,name=iPhone 8"
     - osx_image: xcode9.4
-      env: BUILD_SDK=iphonesimulator11.4 DESTINATION="platform=iOS Simulator,name=iPhone 8"
+      env: SWIFT=4.1 BUILD_SDK=iphonesimulator11.4 DESTINATION="platform=iOS Simulator,name=iPhone 8"
+    - osx_image: xcode9.4
+      env: SWIFT=3.3 BUILD_SDK=iphonesimulator11.4 DESTINATION="platform=iOS Simulator,name=iPhone 8"
     - osx_image: xcode8.3
-      env: VERBOSE=true BUILD_SDK=iphonesimulator10.3 DESTINATION="platform=iOS Simulator,name=iPhone 7"
+      env: SWIFT=3.1 BUILD_SDK=iphonesimulator10.3 DESTINATION="platform=iOS Simulator,name=iPhone 7"
 

Rakefile

@@ -1,5 +1,6 @@
 require 'semver'
 
+SWIFT = ENV['SWIFT'] || '4.1'
 BUILD_SDK = ENV['BUILD_SDK'] || 'iphonesimulator11.4'
 DESTINATION= ENV['DESTINATION'] || 'platform=iOS Simulator,name=iPhone 8'
 EXAMPLE_PROJECT = 'SkyFloatingLabelTextField/SkyFloatingLabelTextField.xcodeproj'
@@ -36,11 +37,11 @@ end
 
 
 task :test do
-  sh "set -o pipefail && xcodebuild test -enableCodeCoverage YES -project #{EXAMPLE_PROJECT} -scheme #{EXAMPLE_SCHEMA} -sdk #{BUILD_SDK} -destination \"#{DESTINATION}\" ONLY_ACTIVE_ARCH=NO | xcpretty"
+  sh "set -o pipefail && xcodebuild test -enableCodeCoverage YES -project #{EXAMPLE_PROJECT} -scheme #{EXAMPLE_SCHEMA} SWIFT_VERSION=#{SWIFT} -sdk #{BUILD_SDK} -destination \"#{DESTINATION}\" ONLY_ACTIVE_ARCH=NO | xcpretty"
 end
 
 task :lint do
-  sh "bundle exec pod lib lint #{VERBOSE ? '--verbose' : ''}"
+  sh "bundle exec pod lib lint --swift-version=#{SWIFT} #{VERBOSE ? '--verbose' : ''}"
   sh "swiftlint"
 end