Let $r_k = \frac{\int_{0}^{1}\left(1-x^7\right)^k dx}{\int_{0}^{1}\left(1-x^7\right)^{k+1} dx}, k \in \mathbb{N}$. Then the value of $\displaystyle \sum_{k=1}^{10}\frac{1}{7\left(r_k-1\right)}$ is equal to: