ogp:profile:first_name always results in a warning to stdout.

[berkes]

Using profile type, as well as some other namespaced attributes, this OGP gem will always issue the warning Some og tag names include colons :, ... removed in the next major version.

The warning then pops up on e.g. logging and consoles. Since it is Kernel#warn, the consumer can disable it, so the problem is minor. Still, this is valid ogp and it is somewhat annoying to see those warnings pop up without being able to do anything about it, other than to disable warnings.

I assume, deprecating this, as announced in that warning, will result in a fix for this issue, so I don't present a PR for it.

If there is anything I can do to help fix this otherwise, or if it is desired to be fixed before it gets deprecated, (e.g. a gsub(':', '_')), please let me know and I'll do so in a PR.