Fix .dll installation directory on Windows

[traversaro]

🦟 Bug fix

Fix .dll installation directory on Windows .

Summary

On Windows, .dll libraries are tipically installed in <prefix>/bin, while before this fix, the .dll libraries were installed by this project in <prefix>/lib, resulting the warning:

Library error: ignition-tools-backward.dll not found. Improved backtrace generation will be disabled

When the ign command was used, as ignition-tools-backward.dll was not found in the directory in which ruby's function to find dll libraries was looking into.

Checklist

• Signed all commits for DCO
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge

[chapulina]

@j-rivero , do you foresee any problems on Linux or macOS?

[j-rivero]

According to documentation:

RUNTIME

    Target artifacts of this kind include:

        Executables (except on macOS when marked as MACOSX_BUNDLE, see BUNDLE below);
        DLLs (on all Windows-based systems including Cygwin; note that the accompanying import libraries are of kind ARCHIVE).

Should affect only DLLs on Windows being backward a library. I don't see problems here.