Build Android debug app on Travis CI

.travis.yml

language: android
sudo: required
jdk: oraclejdk8

branches:
  only:
    - master # build master branch only

before_cache:
  - rm -f  $HOME/.gradle/caches/modules-2/modules-2.lock
  - rm -fr $HOME/.gradle/caches/*/plugin-resolution/
cache:
  directories:
    - $HOME/.gradle/caches/
    - $HOME/.gradle/wrapper/
    - $HOME/.android/build-cache

env:
  global:
    - ANDROID_API=29
    - EMULATOR_API=21
    - ANDROID_BUILD_TOOLS=29.0.2
    - ADB_INSTALL_TIMEOUT=5 # minutes

android:
  components:
    - tools
    - platform-tools
    - build-tools-$ANDROID_BUILD_TOOLS
    - android-$ANDROID_API
    - extra-google-google_play_services
    - extra-google-m2repository
    - extra-android-m2repository

  licenses:
    - 'android-sdk-preview-license-52d11cd2'
    - 'android-sdk-license-.+'
    - 'google-gdk-license-.+'

script: ./gradlew clean assembleDebug --info