Input Lag with a simple game, even with --release

**Bevy version**

0.2.1

**Operating system & version**

Ubuntu 18.04

**What you did**

Working through a very simple bevy tutorial, I noticed significant input lag (with and without rapier).

I boiled an RTC down and uploaded it here: https://github.com/masonk/laggame
Clone that and
`cargo run --release`

This "game" just drives a cube around the screen when you press the arrow keys. Both starting and stopping the cube feels laggy, at least a few hundred ms of input lag, maybe up to 500ms.

I wouldn't be surprised to learn that I'm doing something wrong, but whatever that might be isn't obvious to me.

**What you expected to happen**

I would expect not to feel any input lag in a game this simple.

Additional information:

It shouldn't matter but I'm on monster of a machine, 16 cores, 2080Ti, etc.

Toolchain is recent:
```
mason@mason-threadripper:~/dev/laggame$ rustup show
Default host: x86_64-unknown-linux-gnu
rustup home: /home/mason/.rustup

installed toolchains
--------------------

nightly-2019-12-18-x86_64-unknown-linux-gnu
nightly-2019-12-19-x86_64-unknown-linux-gnu
nightly-x86_64-unknown-linux-gnu (default)

active toolchain
----------------

nightly-x86_64-unknown-linux-gnu (default)
rustc 1.49.0-nightly (ffa2e7ae8 2020-10-24)
```