This is the line that does it:
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" user-scalable="no">
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1" user-scalable="no">
See: https://github.com/h5bp/html5-boilerplate/blob/ed906cfb1b429...