Cho dãy số \[\left( \right):\left\{ {\begin{array}{*{20}{l}}{{u_1} = - 1}\\{{u_{n + 1}} = {u_n} + 3}\end{array}\,\,\left( {\forall n \in \mathbb{N},\,\,n \ge 1} \right)} \right..\] Tính \(\lim \frac{}.\)