build: target API level 28 (Android 9.0 Pie)

Change-Id: I8ddb0f648c4ec3cc82c158a775bb1d230a1eb95b
diff --git a/docker/Dockerfile b/docker/Dockerfile
index 6f0fe7f..26d34a1 100644
--- a/docker/Dockerfile
+++ b/docker/Dockerfile
@@ -51,8 +51,8 @@
 
 # Android SDK libraries, NDK
 ENV ANDROID_DEPS=\
-'build-tools;27.0.3 \
- platforms;android-27 \
+'build-tools;28.0.2 \
+ platforms;android-28 \
  extras;android;m2repository \
  extras;google;m2repository \
  ndk-bundle'