Update build tools in travis config. (#483)

- Use latest available SDK 24 emulator, as tests with generated sources are broken on SDK 19 emulator (`IllegalAccessError`).
- Update to v25 build tools.
- Simplify some commands (emulator script is now built-in, Gradle properly supported).
Source: https://github.com/googlemaps/android-maps-utils/blob/master/.travis.yml

.travis.yml

@@ -1,28 +1,43 @@
 language: android
+jdk: oraclejdk8
 # Use the Travis Container-Based Infrastructure
 sudo: false
-jdk:
-  - oraclejdk8
+
+cache:
+  directories:
+    - ${TRAVIS_BUILD_DIR}/gradle/caches/
+    - ${TRAVIS_BUILD_DIR}/gradle/wrapper/dists/
+
 env:
   global:
-    # increase adb timeout (2 minutes by default)
-    - ADB_INSTALL_TIMEOUT=8
-  matrix:
-    - ANDROID_SDKS=android-23,sysimg-23  ANDROID_TARGET=android-19  ANDROID_ABI=armeabi-v7a
+    - ANDROID_API_LEVEL=24
+    - ANDROID_BUILD_TOOLS_VERSION=25.0.0
+    - ANDROID_ABI=armeabi-v7a
+    - ADB_INSTALL_TIMEOUT=20 # minutes (2 minutes by default)
+
 android:
   components:
+    - tools # to get the new `repository-11.xml`
     - platform-tools
-    - tools
-    - build-tools-23.0.3
-    - android-23
+    - tools # to install Android SDK tools 25.1.x, https://github.com/travis-ci/travis-ci/issues/6040#issuecomment-219367943
+    - build-tools-$ANDROID_BUILD_TOOLS_VERSION
+    - android-$ANDROID_API_LEVEL
+    # Support library
+    - extra-android-support
+    # Latest artifacts in local repository
     - extra-android-m2repository
+    # Specify at least one system image
+    - sys-img-armeabi-v7a-android-$ANDROID_API_LEVEL
+
 before_install:
-  - echo no | android create avd --force -n test -t $ANDROID_TARGET --abi $ANDROID_ABI
-  - emulator -avd test -no-skin -no-audio -no-window &
+  - mkdir "$ANDROID_HOME/licenses" || true
+  - echo -e "\n8933bad161af4178b1185d1a37fbf41ea5269c55" > "$ANDROID_HOME/licenses/android-sdk-license"
+
 before_script:
-  - chmod +x gradlew
-  - chmod +x ./ci/wait_for_emulator
-  - ./ci/wait_for_emulator
-  - adb shell input keyevent 82 &
+  # Create and start emulator
+  - echo no | android create avd --force -n test -t "android-"$ANDROID_API_LEVEL --abi $ANDROID_ABI
+  - emulator -avd test -no-skin -no-window &
+  - android-wait-for-emulator
+
 script:
-    - TERM=dumb ./gradlew connectedCheck
+    - ./gradlew clean connectedCheck --stacktrace