Fix travis for building against JDK 11

Author: Gunbard

.travis.yml

@@ -1,6 +1,11 @@
 language: android
 dist: trusty
 jdk: openjdk11
+env:
+  global:
+    - TARGET_VERSION=30
+    - ANDROID_BUILD_TOOLS_VERSION=30.0.3
+    - ANDROID_HOME=~/android-sdk
 android:
   components:
     # Uncomment the lines below if you want to
@@ -23,10 +28,15 @@ android:
     # if you need to run emulator(s) during your tests
     - sys-img-x86-android-30
 before_install:
-  - chmod +x gradlew
-  - yes | sdkmanager "platforms;android-30"
+  - touch $HOME/.android/repositories.cfg
+  - wget "https://dl.google.com/android/repository/commandlinetools-linux-7302050_latest.zip" -O commandlinetools.zip
+  - unzip commandlinetools.zip -d $ANDROID_HOME/
+  - yes | $ANDROID_HOME/cmdline-tools/bin/sdkmanager "platforms;android-${TARGET_VERSION}" --sdk_root=$ANDROID_HOME
+  - yes | $ANDROID_HOME/cmdline-tools/bin/sdkmanager "build-tools;${ANDROID_BUILD_TOOLS_VERSION}" --sdk_root=$ANDROID_HOME
 install:
   # Skip the default install stage
   - true
+before_script:
+  - chmod +x gradlew
 script:
   - ./gradlew assemble