Fix error in explanation of the interaction between $ and MULTILINE mode.

Reported by Steve Alexander.

Doc/lib/libre.tex

@@ -101,7 +101,7 @@ after each newline.
 newline at the end of the string, and in \constant{MULTILINE} mode
 also matches before a newline.  \regexp{foo} matches both 'foo' and
 'foobar', while the regular expression \regexp{foo\$} matches only
-'foo'.  More interestingly, searching for \regexp{foo\$} in
+'foo'.  More interestingly, searching for \regexp{foo.\$} in
 'foo1\textbackslash nfoo2\textbackslash n' matches 'foo2' normally,
 but 'foo1' in \constant{MULTILINE} mode.