fix: improve ndk home compatibility (#194)

Dockerfile

@@ -34,6 +34,8 @@ ENV ANDROID_NDK_BUCK=${ANDROID_HOME}/ndk/$NDK_VERSION_BUCK
 ENV ANDROID_NDK_GRADLE=${ANDROID_HOME}/ndk/$NDK_VERSION_GRADLE
 # this is needed for Buck to be able to recognize NDK 21
 ENV NDK_HOME=${ANDROID_HOME}/ndk/$NDK_VERSION_BUCK
+ENV ANDROID_NDK_HOME=${ANDROID_HOME}/ndk/$NDK_VERSION_GRADLE
+
 ENV JAVA_HOME=/usr/lib/jvm/java-11-openjdk-amd64
 ENV CMAKE_BIN_PATH=${ANDROID_HOME}/cmake/$CMAKE_VERSION/bin