modules: fix typo in link to upgrading guide

lib/module.c

@@ -99,7 +99,7 @@ static int load_sym_c(struct kr_module *module, uint32_t api_required)
 		/* In case someone re-compiled against new kresd
 		 * but haven't actually changed the symbols. */
 		kr_log_error("[system] module %s requires upgrade.  Please refer to "
-			"https://knot-resolver.readthedocs.io/en/stable/upgrading.hml",
+			"https://knot-resolver.readthedocs.io/en/stable/upgrading.html",
 			module->name);
 		return kr_error(ENOTSUP);
 	}