Let $C$ be the counter-clockwise oriented circle of radius $\frac{1}{2}$ centred at $i=\sqrt{-1}$. Then the value of the contourintegral $\oint_{C} \frac{d z}{z^{4}-1}$ is
1. $-\pi / 2$
2. $\pi / 2$
3. $-\pi$
4. $\pi$