Fix error in book, shared resource need only `Send`
@@ -105,7 +105,7 @@ $ cargo run --target thumbv7m-none-eabi --example lock
{{#include ../../../../ci/expected/lock.run}}
```
-Types of `#[shared]` resources have to be both [`Send`] and [`Sync`].
+Types of `#[shared]` resources have to be [`Send`].
## Multi-lock
