bug#38991: 26.3; Doc string of `mark-end-of-sentence`

[Drew Adams]

  Put mark at end of sentence.  Arg works as in 'forward-sentence'.
                                ^^^
  If this command is repeated, it marks the next ARG sentences after the
  ones already marked.

It would be clearer if "Arg" were "ARG" at the beginning of the second
sentence.


In GNU Emacs 26.3 (build 1, x86_64-w64-mingw32)
 of 2019-08-29
Repository revision: 96dd0196c28bc36779584e47fffcca433c9309cd
Windowing system distributor `Microsoft Corp.', version 10.0.17763
Configured using:
 `configure --without-dbus --host=x86_64-w64-mingw32
 --without-compress-install 'CFLAGS=-O2 -static -g3''