correction arcticle committee.rs (#3360)

add article `a`

Signed-off-by: futreall <86553580+futreall@users.noreply.github.com>

linera-execution/src/committee.rs

@@ -90,7 +90,7 @@ impl<'de> Deserialize<'de> for ValidatorName {
     }
 }
 
-/// Public state of validator.
+/// Public state of a validator.
 #[derive(Eq, PartialEq, Hash, Clone, Debug, Default, Serialize, Deserialize)]
 pub struct ValidatorState {
     /// The network address (in a string format understood by the networking layer).