options: fix typo

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/options.c

@@ -956,7 +956,7 @@ bool get_cfg(options_t *opt, int argc, char *const *argv, bool shadow_enable,
 		if (!opt->experimental_backends) {
 			log_warn("Dual-kawase blur is not implemented by the legacy "
 			         "backends, you must use the `experimental-backends` "
-			         "option`.");
+			         "option.");
 		}
 	}