Change to API 23.

Author: Mike Ng

.travis.yml

@@ -4,10 +4,10 @@ android:
     - tools
     - platform-tools
     - build-tools-24.0.3
-    - android-24
-    - doc-24
+    - android-23
+    - doc-23
     - extra-android-m2repository
-    - sys-img-armeabi-v7a-android-24
+    - sys-img-armeabi-v7a-android-23
 jdk:
   - oraclejdk8
 before_cache:
@@ -19,7 +19,7 @@ cache:
 before_script:
   - echo $TRAVIS_BRANCH
   - echo $TRAVIS_TAG
-  - echo no | android create avd --force -n test -t android-24 --abi default/armeabi-v7a
+  - echo no | android create avd --force -n test -t android-23 --abi default/armeabi-v7a
   - emulator -avd test -no-audio -no-window &
   - android-wait-for-emulator
   - adb shell input keyevent 82 &