Referncing a java script inside my master page will not work

I have added the following to my seatle.master page inside my SharePoint server 2013 :-

<SharePoint:ScriptLink language="javascript" name="custom.js" OnDemand="true" runat="server" Localizable="false" />

an i added the custom.js file inside the following path:- C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\15\TEMPLATE\LAYOUTS

The script is a simple function to display the current date inside a div , as follow:-

$( document ).ready(function() {


document.getElementById("currentdate").innerHTML = formatAMPM();

function formatAMPM() {
var d = new Date(),
    minutes = d.getMinutes().toString().length == 1 ? '0'+d.getMinutes() : d.getMinutes(),
    hours = d.getHours().toString().length == 1 ? '0'+d.getHours() : d.getHours(),
    ampm = d.getHours() >= 12 ? 'pm' : 'am',
    months = ['Jan','Feb','Mar','Apr','May','Jun','Jul','Aug','Sep','Oct','Nov','Dec'],
    days = ['Sun','Mon','Tue','Wed','Thu','Fri','Sat'];
return days[d.getDay()]+' '+d.getDate()+' '+months[d.getMonth()]+' '+d.getFullYear()+' '+hours+':'+minutes+' '+ampm;
}
});

baring in mind if i add script editor web part inside the page and i added the above code, it will show the current date and time. but having this code inside a script editor web part mean that i have to add this web part to all my pages, instead i want this script to fire for all the site collection pages. any idea how to solve this issue ?