Add missing brace to .js and add some perf improvements

A closing brace for the "if" statement was missing. Added that, then decided to do some other performance improvements.

The new implementation memoizes the name list into the function once. This helps it avoid allocating a new array in memory every time the function is called.

It also uses the Array.indexOf function if it is available, rather than looping through the array manually.

Tested with the following code, which shows a 33% speed improvement over the previous implementation.

```html
<!DOCTYPE html>
<html>
<head>
	<script src="isGirl.js"></script>
	<script type="text/javascript">
	
	// Basic name check
	console.log('isGirl(zina) should be true and is ' + isGirl('zina'));
	console.log('isGirl(zinaz) should be false and is ' + isGirl('zinaz'));
	
	// Try it with a missing 'indexOf' function
	console.log('Switching to non-indexOf implementation');
	var temp = Array.prototype.indexOf;
	delete Array.prototype.indexOf;
	console.log('isGirl(zina) should be true and is ' + isGirl('zina'));
	console.log('isGirl(zinaz) should be false and is ' + isGirl('zinaz'));
	Array.prototype.indexOf = temp;
	
	// Test Performance
	console.log('How long does it take to call isGirl() a million times?');
	var start = new Date().getTime();
	for (var i = 0; i < 1000 * 1000; i++) {
		isGirl('zina');
	}
	var end = new Date().getTime();
	console.log( 'It takes ' + (end-start) + ' milliseconds to call isGirl() million times');
	</script>
</head>
</html>
```