Update Android SDK Build Tools version for travis

- auto-accept license for newer version

Author: Albert Wu

.travis.yml

@@ -2,9 +2,12 @@ language: android
 
 android:
   components:
-  - build-tools-27.0.3
+  - build-tools-28.0.3
   - android-26
 
+before_install:
+  - yes | sdkmanager "build-tools;28.0.3"
+
 script:
   - ./gradlew test
 
@@ -17,4 +20,4 @@ env:
   - secure: hLpLbEi5ThL/+qHuEmJvvJkzfBrXbyOjDbd9fSSYESSQuGUoEGH3UM7Ws6eJynv/G0w+xmJIQ4vlDbSBa53vaYwHB2l0Rhcoj3XHHvpMwlckIh/TGA+o4Bd5DHN61Jatm6ja8PFRAhNF4adsLUwObrE6Z9ydepKFYBWSjP4xEws=
 
 git:
-  depth: 9999999
+  depth: 9999999