Set MSRV to 1.53

[brainstorm]

Otherwise, it breaks like so: rust-lang/rfcs#2818 (comment)

[popzxc]

Thanks for creating this issue! Totally forgot to do it.

Note that if you need this crate to work with the rustc 1.52 or older, it's possible to use v0.2 (which also has the macro for getting function name, but is not bound on the recent compiler).