update NDK to r19b

Nothing interesting.  We were already on r19's beta.

Change-Id: I4d58e7f82317427d06ef5b138681c00b476ecd9a
Reviewed-on: https://skia-review.googlesource.com/c/193469
Commit-Queue: Mike Klein <mtklein@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: Mike Klein <mtklein@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
7 files changed