Bump Travis version

Author: Roger Hu

.travis.yml

@@ -6,12 +6,14 @@ android:
   components:
   - tools
   - platform-tools
-  - build-tools-25.0.3
-  - android-25
+  - build-tools-27.0.3
+  - android-27
   - extra-android-m2repository
   - extra-google-m2repository
   licenses:
   - android-sdk-license-.+
+before_install:
+  - yes | sdkmanager "platforms;android-27"
 script:
 - "./gradlew build check --daemon"
 after_failure: "cat $TRAVIS_BUILD_DIR/app/build/outputs/lint-results.xml"