Express sum as a definite integral

Homework Statement

If n is a positive integer, then
$$\lim_{n\to\infty}\frac{1}{n}\left[\left(\frac{1}{n}\right)^2+\left(\frac{2}{n}\right)^2+\cdot\cdot\cdot+\left(\frac{n-1}{n}\right)^2\right]$$can be expressed by what definite integral?

The attempt at a solution

A student I was helping had this problem and I had no idea how to even start. It was a problem along with other basic calc I definite and indefinite integrals, so I'm guessing it has some easy solution that I'm completely missing.