Fix docker run script in all contract README

[ethanfrey]

We no longer need something like:

docker run --rm -v "$(pwd)":/code \
  --mount type=volume,source="cosmwasm_plus_cache",target=/code/target \
  --mount type=volume,source=registry_cache,target=/usr/local/cargo/registry \
  cosmwasm/rust-optimizer:0.9.0 ./contracts/cw20-atomic-swap

but rather:

docker run --rm -v "$(pwd)":/code \
  --mount type=volume,source="cosmwasm_plus_cache",target=/code/target \
  --mount type=volume,source=registry_cache,target=/usr/local/cargo/registry \
  cosmwasm/workspace-optimizer:0.10.2 

And the output is artifacts/cw20_staking.wasm

This should be updated in all contracts

[maurolacy]

PR: #71.