Minimal number system

Task

Implement function, that for given value n returns minimal base, in which n will includes only 1.

getBase('13') // -> '3', because 13 in 3 number system is 111
getBase('4681') // -> '8', because 4681 in 8 number system is 11111
getBase('1000000000000000000') // -> '999999999999999999', because 1000000000000000000 in 999999999999999999 number system is 11

Write your code in src/index.js