Backport commit 08782a2 from Emacs master branch

Prefer plain characters to Texinfo circumlocutions
08782a2ea95dec5662954a1de353a7da699ac339
Paul Eggert
Fri May 1 12:58:53 2015 -0700

doc/org.texi

@@ -18485,7 +18485,7 @@ enabled source code highlighting in Gnus.
 Max-Planck-Institute for Neurology.  He also inspired the creation of a
 concept index for HTML export.
 @item
-@i{J@"urgen Vollmer} contributed code generating the table of contents
+@i{Jürgen Vollmer} contributed code generating the table of contents
 in HTML output.
 @item
 @i{Samuel Wales} has provided important feedback and bug reports.