Escape dashes in xzmore.1

A minus sign is larger, easier to see in a printout, and more
likely to use the same glyph as ASCII hyphen-minus in a terminal
than a hyphen.  Since broken manual pagers do not find hyphens
when the user searches for a hyphen-minus, minus signs are also
easier to search for.  So use minus signs instead of hyphens to
render sample terminal output.

src/scripts/xzmore.1

@@ -31,14 +31,14 @@ The name
 is provided for backward compatibility with LZMA Utils.
 .TP
 .BR e " or " q
-When the prompt --More--(Next file:
+When the prompt \-\-More\-\-(Next file:
 .IR file )
 is printed, this command causes
 .B xzmore
 to exit.
 .TP
 .B s
-When the prompt --More--(Next file:
+When the prompt \-\-More\-\-(Next file:
 .IR file )
 is printed, this command causes
 .B xzmore