Pass --cap-lints=warn to the RUSTFLAGS

It is simply impossible to fight against people putting
 #![deny(warnings)] into the code…

Closes: https://pagure.io/fedora-rust/rust2rpm/issue/98
Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>

data/macros.rust

@@ -7,6 +7,7 @@
   -Cdebuginfo=2
   -Clink-arg=-Wl,-z,relro,-z,now
   -Ccodegen-units=1
+  --cap-lints=warn
 }
 
 %__global_rustflags %{build_rustflags}