This is my code, I can't find the bug.

/* 
These are the arrays needed to store the user answers as 
correct and incorrect, and there is the array to store 
the questions and correct answers.
*/

var user_answer;
var correct_answer = [ ];
var incorrect_answer = [ ];
var questions_answers = [
  ["How many continents are there?", "7"],
  ["What is the capital of France?", "Paris"],
  ["Who is the president of the USA?", "Donald Trump"]
];

// This function prints an array as a numbered list

function printList( list ) {
  var listHTML = '<ol>';
  for (var i = 0; i < list.length; i += 1) {
    listHTML += '<li>' + list[i] + '</li>';
  }
  listHTML += '</ol>';
  print(listHTML);
}

// Replaces document.write

function print(message) {
  document.write(message);
}

/*This is the loop that asks and checks the questions, 
this is what isn't working
*/

for (var i = 0; i < 3; i +=1) {
  user_answer = prompt(questions_answers[i][0]);
  if ( user_answer.toLowerCase === questions_answers[i][1].toLowerCase ) {
   correct_answer.push( questions_answers[i][0] );
  } else {
   incorrect_answer.push( questions_answers[i][0] );
  }
}

// What will show after the user answers

print("<h2>You got these questions right!</h2>");
printList( correct_answer );
print("<h2>You got these questions wrong.</h2>");
printList( incorrect_answer );