Number to Hexadecimal

Problem

Given a non-negative integer n, convert it to a hexadecimal string. The returned hexadecimal string must not have leading zeroes, except for the number zero itself.

Examples

toHex(10)
// returns "a"
// 10 in decimal equals "a" in hexadecimal.

toHex(16)
// returns "10"
// 16 in decimal is "10" in hexadecimal.

toHex(255)
// returns "ff"
// 255 in decimal is "ff" in hexadecimal.