Show the sum of n zero-mean stationary random variables is bounded by $\mathcal{O}(\sqrt{n})$

Question

Let $\{X_t\}$ be a zero-mean stationary process with absolutely summable autocovariance function satisfying $\sum_{-\infty}^{\infty}\gamma(h)=0$.

Show that $\sum_{t=1}^nX_t=\mathcal{O(\sqrt{n})}$.