Fix docker release

[mgrachev]

error[E0658]: use of unstable library feature 'str_strip': newly added
  --> src/common/comment.rs:17:10
   |
17 |         .strip_prefix(format!("{}:", PREFIX).as_str())?
   |          ^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/67302

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.
error: could not compile `dotenv-linter`.
warning: build failed, waiting for other jobs to finish...
error: failed to compile `dotenv-linter v2.2.0 (/usr/src/dotenv-linter)`, intermediate artifacts can be found at `/usr/src/dotenv-linter/target`

✔ Checklist:

• This PR has been added to CHANGELOG.md (at the top of the list);
• Tests for the changes have been added (for bug fixes / features);
• Docs have been added / updated (for bug fixes / features).