message: travis: try NDK r21d update
diff: @@ -50,10 +50,10 @@ before_install:
  # android ndk: download and create toolchain
  - if [ $os_build == "android" ]; then
  - wget -nv -O android-ndk.zip https://dl.google.com/android/repository/android-ndk-r21-linux-x86_64.zip;
  + wget -nv -O android-ndk.zip https://dl.google.com/android/repository/android-ndk-r21d-linux-x86_64.zip;
  echo "Extracting NDK...wait";
  unzip -qq android-ndk.zip;
  - export NDK=$PWD/android-ndk-r21;
  + export NDK=$PWD/android-ndk-r21d;
  $NDK/build/tools/make_standalone_toolchain.py --arch $os_arch --api $android_api --stl libc++ --install-dir android-toolchain;
  export ANDROID_TOOLCHAIN=$PWD/android-toolchain;
  fi
  