[doc] fix incorrect param name

[stas00]

Invalid param name

Thanks.

[jeffra]

Good catch

[stas00]

Is there are reason why you use this weird markdown:

***loss\_scale\_window***

and not just:

**loss_scale_window**

I'm not sure why you had to do that in first place, but it also prevents grep from working and finding such bugs as fixes in this PR.

edit or I see - it's for bold+italics - let's see if there is a better way

Looks like github fixed their parser to do the right thing with ***A_B***. test: A_B

But if your doc builder doesn't - this is probably a more sustainable approach: <i>**A_B**</i> test: A_B

[stas00]

Here is a little perl magic to quickly rewrite your docs, e.g. on:

perl -pi -e 'BEGIN{ sub a{$_=$_[0]; ~s|\\||g; $_}} s|\*\*\*(\S+)\*\*\*|"<i>**".a($1)."**</i>"|msge' docs/_pages/config-json.md

To change all .mds:

find . -name "*md" -exec perl -pi -e 'BEGIN{ sub a{$_=$_[0]; ~s|\\||g; $_}} s|\*\*\*(\S+)\*\*\*|"<i>**".a($1)."**</i>"|msge' {} \;

it seems to change just 2 files.

Proposal: #775