How to get no frame on a table in AsciiDoc on GitHub

Question

I want to make a table in AsciiDoc on GitHub with no frame. My reading of the documentation is that this should work:

[frame="none",options="header"]
|===
| Foo | Bar
| Widget | Gadget
|===

Yet it renders with a frame:

That frame="none" setting should do it. But it doesn't. I try it without quotes and its the same. The options="header" works fine, so I know the interpreter is seeing the line in brackets and taking some action.

Is it possible that GitHub runs some version of AsciiDoc that is not full featured? If so, is there a site with the details of what does and doesn't work?

Note--this is on our internal corporate instance of GitHub Enterprise, so we may be some versions out of date, or not have some plug-in installed. Is there a special plug-in that does the trick? I don't admin the platform, so is there a way I can check versions and plug-ins in any given GitHub platform as an ordinary developer?

We use AsciiDoc pervasively as our GitHub Wiki language, so changing to another one that does tables better is not an option.

All help appreciated!