Update structopt to 0.3.26 am: 12ae7f8ab5 am: 8a646ada9d am: 1b851c6441 am: b6ead5beb7

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt/+/2004098

Change-Id: Iea1433af09d8788cc06f0331e2795a24cb79e860