Using NDK r21 (release) on Travis CI

.travis.yml

@@ -6,10 +6,10 @@ install:
   - curl https://dl.google.com/android/repository/sdk-tools-linux-4333796.zip --output $HOME/android-sdk.zip
   - unzip -qq $HOME/android-sdk.zip -d $HOME/android-sdk
   - export ANDROID_SDK_HOME=$HOME/android-sdk
-  - export ANDROID_NDK_HOME=$ANDROID_SDK_HOME/ndk/20.1.5948944
+  - export ANDROID_NDK_HOME=$ANDROID_SDK_HOME/ndk/21.0.6113669
   # Installing necessary components of Android SDK
   - function installAndroidComponent() { yes | ${ANDROID_SDK_HOME}/tools/bin/sdkmanager $1 > /dev/null; }
-  - installAndroidComponent "ndk;20.1.5948944"
+  - installAndroidComponent "ndk;21.0.6113669"
   - installAndroidComponent "cmake;3.10.2.4988404"
   # Installing meson, ninja and nasm that are necessary for libdav1d building
   - sudo apt-get install python3-pip python3-setuptools python3-wheel ninja-build