isSubsequence = function(s, t) {
    for (let char of s) {
        let indexChar = t.indexOf(char);
        if (indexChar === -1) {
            return false;
        }
        t = t.slice(indexChar+1);
    }
    return true
}
Time O(N^2) | Space O(1)
@param {string} s
@param {string} t
@return {boolean}