org: work around issue with Org 9.2

See the following email
http://lists.gnu.org/archive/html/emacs-orgmode/2019-01/msg00226.html

* doc/org/tut24.org, doc/org/tut51.org: Export the output of
noweb-based block without ':export results' or ':export both'.
* doc/org/spot.css: Add style for src-text.
13 jobs for next in 150 minutes and 21 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed alpine-gcc #28006

00:26:41

passed arch-clang #28007

00:42:28

passed arch-gcc-glibcxxdebug #28008

00:53:22

passed debian-gcc-snapshot #28005

01:04:05

passed debian-stable-gcc #28003

00:35:49

passed debian-unstable-gcc-coverage #28004

00:44:59

88.8%
passed debpkg-stable #28011

02:28:11

passed debpkg-unstable #28012

02:06:28

passed mingw-shared #28009

00:16:26

passed mingw-static #28010

00:14:22

passed rpm-pkg #28013

00:51:00

 
  Publish
passed publish-rpm #28014
dput

00:00:22

passed publish-unstable #28015
dput

00:01:45