Use heck-0.3.3 am: 960abda7c6

Original change: https://android-review.googlesource.com/c/platform/external/rust/crates/structopt-derive/+/2209805

Change-Id: I25660cc29c1339da319c7785d2a2d9ad2c84b625
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>