Stack docs incorrectly specify that `category` axis is not supported

[archiewood]

The docs say:

echarts-doc/en/option/series/bar.md

Line 144 in 5b063b0

Notice: `stack` only supports stacking on `value` and `log` axis for now. `time` and `category` axis are not supported.

Notice: stack only supports stacking on value and log axis for now. time and category axis are not supported.

However, I believe this is incorrect, category is supported

apache/echarts#7937 (comment)