build cleanly with nightly Rust 2021-03-14+

The CI nightly builds had been broken with the following error:

```
error: custom inner attributes are unstable
  --> /home/runner/work/moonfire-nvr/moonfire-nvr/server/target/debug/build/moonfire-db-415ce696a754c614/out/schema.rs:10:4
   |
10 | #![rustfmt::skip]
   |    ^^^^^^^^^^^^^
   |
   = note: `#[deny(soft_unstable)]` on by default
   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
   = note: for more information, see issue #64266 <https://github.com/rust-lang/rust/issues/64266>
```

I'd thought this was by mistake given that #[rustfmt::skip] is still
advertised on rustfmt's github page, but maybe not. Looks like
rust-protobuf's newest version uses
`#![cfg_attr(rustfmt, rustfmt::skip)]` to avoid this error.

Also fix a warning on nightly about an extraneous semicolon.

CHANGELOG.md

@@ -6,6 +6,10 @@ changes, see Git history.
 Each release is tagged in Git and on the Docker repository
 [`scottlamb/moonfire-nvr`](https://hub.docker.com/r/scottlamb/moonfire-nvr).
 
+## `v0.6.3` (in progress)
+
+*   Compile fix for nightly rust 2021-03-14 and beyond.
+
 ## `v0.6.2`
 
 *   Fix panics when a stream's PTS has extreme jumps