android build: bump targetSdkVersion to 29 (follow-up)

follow-up: 59e9337be0

For some reason, without this change, the first build works but subsequent builds fail.
Not sure what the cause is. This is why Travis builds work.

contrib/android/Dockerfile

@@ -67,7 +67,7 @@ RUN yes | ${ANDROID_SDK_MANAGER} --licenses > /dev/null
 
 # download platforms, API, build tools
 RUN ${ANDROID_SDK_MANAGER} "platforms;android-24" > /dev/null && \
-    ${ANDROID_SDK_MANAGER} "platforms;android-28" > /dev/null && \
+    ${ANDROID_SDK_MANAGER} "platforms;android-29" > /dev/null && \
     ${ANDROID_SDK_MANAGER} "build-tools;${ANDROID_SDK_BUILD_TOOLS_VERSION}" > /dev/null && \
     ${ANDROID_SDK_MANAGER} "extras;android;m2repository" > /dev/null && \
     chmod +x "${ANDROID_SDK_HOME}/tools/bin/avdmanager"

contrib/android/buildozer.spec

@@ -70,7 +70,8 @@ fullscreen = False
 # (list) Permissions
 android.permissions = INTERNET, CAMERA, WRITE_EXTERNAL_STORAGE
 
-# (int) Android API to use  (targetSdkVersion)
+# (int) Android API to use  (targetSdkVersion AND compileSdkVersion)
+# note: when changing, Dockerfile also needs to be changed to install corresponding build tools
 android.api = 29
 
 # (int) Minimum API required. You will need to set the android.ndk_api to be as low as this value.