nimble lock fails when there are local changes
That could happen when the main project is in dev mode:

```
       Tip: 1 messages have been suppressed, use --verbose to show them.
nimble.nim(1534)         validateDevModeDepsWorkingCopiesBeforeLock

    Error:  Some of package's develop mode dependencies are invalid.
        ... Package "codex" at "/home/yyoncho/Sources/nim/nim-workspace/nim-codex" has not clean working copy..
     Hint:  When you are using a lock file Nimble requires develop mode dependencies to be under version control, all local changes to be committed and pushed on some remote, and lock file to be updated.
```