man_show_fixme.sh: Fix rendering issue

If a single quote falls at the start of a line, then the rest of
the line is treated as a comment. Therefore, escape single quotes.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

scripts/man_show_fixme.sh

@@ -41,6 +41,7 @@ for f in $*; do
         fixme == 1 {
 	    sub("^\\...[ ]", "")
 	    sub("^\\...", "")
+	    gsub("'"'"'", "\\(aq")
             if ($0 ~ /^[ 	][ 	]*.*/) {
                 print ".br"
                 sub("^[ 	]*", "    ")