message: Update ERC20 E2E tests for `LangError` changes
  The original PR for the ERC20 E2E tests had been sitting around a bit
  long and didn't account for the extra `Result`. I should've merged
  `master` into the PR before merging, haha.
diff: @@ -574,10 +574,14 @@ mod erc20 {
  // then
  assert_eq!(
  total_supply,
  - total_supply_res.value.unwrap(),
  + total_supply_res.return_value().unwrap(),
  "total_supply"
  );
  - assert_eq!(transfer_to_bob, balance_of_res.value.unwrap(), "balance_of");
  + assert_eq!(
  + transfer_to_bob,
  + balance_of_res.return_value().unwrap(),
  + "balance_of"
  + );
  Ok(())
  }
  @@ -664,7 +668,7 @@ mod erc20 {
  assert_eq!(
  total_supply - approved_value,
  - balance_of_res.value.unwrap(),
  + balance_of_res.return_value().unwrap(),
  "balance_of"
  );
  