Leave specific Rust version numbers out for now

Until 1.0?

Signed-off-by: Neal McBurnett <nealmcb@gmail.com>

Author: nealmcb

docs/content/quickstart.md

@@ -196,7 +196,6 @@ Successfully ran the build command for the Spin components.
 > For more details, see the [page about developing Spin applications](./developing.md).
 
 If you run into errors, you might want to use `rustup check` to see if your Rust installation is up-to-date.
-This quickstart is known to work with Rust version 1.64.
 
 ## Running the application with `spin up`