Added RWMutex to keysWithExpiry in order to improve thread safety

src/raft/raft.go

@@ -119,6 +119,10 @@ func (r *Raft) RaftInit(ctx context.Context) {
 	}
 
 	r.raft = raftServer
+
+	// TODO
+	// Listen on leadership change channel and initiate key eviction goroutine
+	// if current node is the leader.
 }
 
 func (r *Raft) Apply(cmd []byte, timeout time.Duration) raft.ApplyFuture {