The value of the integral \( \displaystyle \int_{-\pi/2}^{\pi/2} \frac{dx}{(1+e^{x})(\sin^{6}x+\cos^{6}x)} \) is equal to:
\( 2\pi \)
\( 0 \)
\( \pi \)
\( \frac{\pi}{2} \)