Prove that $\lim_{n\rightarrow \infty} \int_{[0,1]^n}\frac{|x|}{\sqrt{n}}=\frac{1}{\sqrt{3}}$

Prove that $$\lim_{n\rightarrow \infty} \int_{[0,1]^n}\frac{|x|}{\sqrt{n}}=\frac{1}{\sqrt{3}},$$
where $[0,1]^n=[0,1]\times \dots \times [0,1]$ is the unit cube in $\mathbb{R}^n$. 

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