Using GMaps.js for integrating Google Maps API - can't see where to add my API Key

I am using the GMaps.js library and the code I am using is working 100% fine (running locally on localhost) - the 'webapp' I have created also uses the Google Maps Geocoding API.

I cannot see where I add my API keys anywhere within my code - although I am kinda confused as it currently works? Surely it should only work with a valid API key.

https://hpneo.github.io/gmaps/

<!DOCTYPE html>
<html>
<head>
<link href='example.css' rel='stylesheet' type='text/css' />
<link rel="stylesheet" type="text/css" href="style/style.css">
<script type="text/javascript" src="gmaps.js"></script>
<script type="text/javascript">
  map = new GMaps({
    div: '#map',
    lat: 52.4801,
    lng: -1.8835,
    zoom: 7
  });
</script>
</head>
<body>
<div id="map"></div>
</body>
</html>

Solution

Ok - i have found the answer here: When is a Google Maps API key required?

In a nutshell version 3 doesn't require an API (v2 did) but it is recommended from what other developer are saying in regards to setting them up.