message: Use new crate name cosmwasm-std in 0.8.0 CHANGELOG
diff: - Return value from `env.write_db` and `env.remove_db` to allow error reporting.
  - Query responses are now required to contain valid JSON.
  -**cosmwasm**
  +**cosmwasm-std**
  - Make all symbols from `cosmwasm::memory` crate internal, as those symbols are
  not needed by users of the library.
  