example/bind/android: update gradle version
example/bind/android: update gradle version

from 0.2.2 to 0.2.3

Change-Id: I906200acf9615c8cc100b7d1ad5592e899e383fe
Reviewed-on: https://go-review.googlesource.com/19409
Reviewed-by: David Crawshaw <a2f0bf29257797dd66800b4fbb9945c3e216c004@golang.org>

golang/mobile,golang/mobile,golang/mobile,golang/mobile