[LyX/master] Update Russian localization

[Juergen Spitzmueller]

commit 86a4d6c8abec83070b5d6be58373d3ee4ebde532
Author: Yuriy Skalko <yuriy.skalko at gmail.com>
Date:   Sun Aug 2 21:50:52 2020 +0300

    Update Russian localization

 lib/doc/ru/Math.lyx      |   87 +++---
 lib/doc/ru/UserGuide.lyx |  776 ++++++++++++++++++++++++----------------------
 po/ru.po                 |  124 ++++----
 3 files changed, 516 insertions(+), 471 deletions(-)