leaflet map not showing completely

I started working on leaflet map but i am stuck in very odd problem.map is loading but only top tiles of map are showing.bottom portion of the div is gray.

    map = L.map('map-container', {
       center: [123.00, -79.00],
        minZoom: 2,
        zoom: 10,
       tileSize:756
    });

    L.tileLayer('http://ift.tt/UdqNor', {
        attribution: '&copy; <a href="http://ift.tt/1tfsXTk">OpenStreetMap</a>',
        subdomains: ['a', 'b', 'c']
        }).addTo(map);

I am getting the map as the image shown