Write a function named intersection(firstArr) that takes in an array and
returns a function. When the function returned by intersection is invoked
passing in an array (secondArr) it returns a new array containing the elements
common to both firstArr and secondArr.

Example 1:
let abc = intersection(["a", "b", "c"]); // returns a function
console.log(abc(["b", "d", "c"])); // returns [ 'b', 'c' ]

Example 2:
let fame = intersection(["f", "a", "m", "e"]); // returns a function
console.log(fame(["a", "f", "z", "b"])); // returns [ 'f', 'a' ]

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function intersection(firstArr) {
  return (secondArr) => {

    let common = [];

    for (let i = 0; i < firstArr.length; i++) {
      let el = firstArr[i];
      if (secondArr.indexOf(el) > -1) {
        common.push(el);
      }
    }

    return common;

  }; 
}