Incorrect comma inserted in cfg (CI only)

[nrc]

E.g.,

#[cfg(not(all(feature="std",
              any(target_os = "linux", target_os = "android",
                  target_os = "netbsd",
                  target_os = "dragonfly",
                  target_os = "haiku",
                  target_os = "emscripten",
                  target_os = "solaris",
                  target_os = "cloudabi",
                  target_os = "macos", target_os = "ios",
                  target_os = "freebsd",
                  target_os = "openbsd", target_os = "bitrig",
                  target_os = "redox",
                  target_os = "fuchsia",
                  windows,
                  all(target_arch = "wasm32", feature = "stdweb"),
                  all(target_arch = "wasm32", feature = "wasm-bindgen"),
))))]
type Os = NoSource;

Changes the last line to ),))].

I can't reproduce this locally, but it seems to be causing rand to fail testing in CI.

[topecongiro]

https://github.com/rust-lang-nursery/rustfmt/blob/1c408818c8a752dd584e7858b4afd3ceb011a7da/src/attr.rs#L221-L223

This assumption does not stand when the attribute is nested, and causes rustfmt to be non-idempotent.