fix(sexp): Accept another digit after an \x.. or \... escape sequence…

… in strings

The two cases that this modifies are meant to catch the issue of
"unterminated ... escape sequences" but, due to the use of '*', they
also caught the cases where the escape sequence was followed by another
digit

Signed-off-by: Samuel Hym <samuel.hym@rustyne.lautre.net>

src/dune_sexp/lexer.mll

@@ -320,15 +320,15 @@ and escape_sequence = parse
   | digit digit digit
     { error lexbuf "escape sequence in quoted string out of range" ~delta:(-1);
     }
-  | digit*
+  | digit digit?
     { error lexbuf "unterminated decimal escape sequence" ~delta:(-1);
     }
   | 'x' (hexdigit as c1) (hexdigit as c2)
     { let v = eval_hex_escape c1 c2 in
       Template.Buffer.add_text_c (Char.chr v);
       Other
     }
-  | 'x' hexdigit*
+  | 'x' hexdigit?
     { error lexbuf "unterminated hexadecimal escape sequence" ~delta:(-1);
     }
   | _