Truncate UIDs and GIDs larger than 999999 (rev2)

[gregoster]

Truncate UIDs and GIDs larger than 999999 so they do not overflow the 6-character field. (Second version. Replaces #31 )

[mdsteele]

Looks good, thanks. Could you also add a new unit test to the bottom of builder.rs? Something kind of like this one, but setting UID/GID to some values > 999999, with the expected text showing the expected truncation.

[mdsteele]

(Also, note that you don't need to open a new pull request to make changes; you can just push more changes to your same branch.)

[gregoster]

Done! And ya, I'm still figuring out github workflows too :)

[mdsteele]

Thanks!