Bump Android NDK to 20 and update buck(#58)

* bump NDK to r20, buck to 2019.06.17.01

* bump buck to 2019.09.03.01, ndk to 20

Author: dulmandakh

Dockerfile

@@ -6,8 +6,8 @@ LABEL Description="This image provides a base Android development environment fo
 ARG SDK_VERSION=sdk-tools-linux-4333796.zip
 ARG ANDROID_BUILD_VERSION=28
 ARG ANDROID_TOOLS_VERSION=28.0.3
-ARG BUCK_VERSION=2019.05.22.01
-ARG NDK_VERSION=19c
+ARG BUCK_VERSION=2019.09.03.01
+ARG NDK_VERSION=20
 ARG NODE_VERSION=10.x
 ARG WATCHMAN_VERSION=4.9.0