[CI] Test with swift-4.2-DEVELOPMENT-SNAPSHOT on Linux

Author: ikesyo

.travis.yml

@@ -61,6 +61,19 @@ jobs:
         - swift test
       git:
         submodules: false
+    - os: linux
+      language: generic
+      sudo: required
+      dist: trusty
+      env: SWIFT_VERSION=4.2-DEVELOPMENT-SNAPSHOT-2018-06-12-a
+      before_install:
+        - eval "$(curl -sL https://gist.githubusercontent.com/kylef/5c0475ff02b7c7671d2a/raw/9f442512a46d7a2af7b850d65a7e9bd31edfb09b/swiftenv-install.sh)"
+      script:
+        - swift --version
+        - swift build
+        - swift test
+      git:
+        submodules: false
     - stage: carthage
       script: carthage build --cache-builds --no-skip-current
     - stage: deploy