Use heck-0.3.3 am: 960abda7c6 am: 8d4f507515 am: 5639047125 am: 3c96ba54d5

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

Change-Id: I76e61bc7369be5c06de14744915272b34b31d088
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>