Add Xcode 9 job

Author: ikesyo

.travis.yml

@@ -11,6 +11,12 @@ matrix:
       script:
         - set -o pipefail && xcodebuild -workspace "$TRAVIS_XCODE_WORKSPACE" -scheme "$TRAVIS_XCODE_SCHEME" test | xcpretty
       env: JOB=Xcode8
+    - os: osx
+      osx_image: xcode9
+      xcode_scheme: ReactiveTask
+      script:
+        - set -o pipefail && xcodebuild -workspace "$TRAVIS_XCODE_WORKSPACE" -scheme "$TRAVIS_XCODE_SCHEME" test | xcpretty
+      env: JOB=Xcode9
     - os: osx
       osx_image: xcode8.3
       script: