Add vote-update-validator subcommand

programs/vote/src/vote_instruction.rs

@@ -58,7 +58,7 @@ pub enum VoteInstruction {
     /// Withdraw some amount of funds
     Withdraw(u64),
 
-    /// Update the vote account's node id
+    /// Update the vote account's validator identity (node id)
     UpdateNode(Pubkey),
 }