Add allow warnings for nonstandard macro braces

The warnings come from the macros of libraries that we use, so we can't
change them.

app/src/lib.rs

@@ -1,4 +1,5 @@
 #![recursion_limit = "256"]
+#![allow(clippy::nonstandard_macro_braces)]
 mod api;
 mod app;
 mod cookies;