delta.c: fix option '-t'

Both the help and man page claims that it accepts -t with an argument
so let's do that.

src/delta/delta.c

@@ -352,7 +352,7 @@ static int parse_argv(int argc, char *argv[]) {
         assert(argc >= 1);
         assert(argv);
 
-        while ((c = getopt_long(argc, argv, "h", options, NULL)) >= 0) {
+        while ((c = getopt_long(argc, argv, "ht:", options, NULL)) >= 0) {
 
                 switch (c) {