Fix `cargo contract new` template build
Created by: cmichi
Closes https://github.com/paritytech/ink/issues/705.
We have a test for cargo contract new
, but the test is currently not run in CI. I've created https://github.com/paritytech/cargo-contract/pull/180 to fix this. This PR here is a pre-requirement to make the test run in CI again though. So after we have merged this PR I can update the other one.