Not changed cluster image after changing default cluster's number in gmap3

Question

I have used below code for clusters but in this situation cluster-3 is not display and display only cluster-1 and cluster-2.

clusters: {
    // This style will be used for clusters with more than 0 markers
    10: {
        content: '<div class="cluster cluster-1">CLUSTER_COUNT</div>',
        width: 53,
        height: 52
    },
    // This style will be used for clusters with more than 20 markers
    50: {
        content: '<div class="cluster cluster-2">CLUSTER_COUNT</div>',
        width: 56,
        height: 55
    },
    // This style will be used for clusters with more than 50 markers
    100: {
        content: '<div class="cluster cluster-3">CLUSTER_COUNT</div>',
        width: 66,
        height: 65
    }
},

Here remaining code is same like in css and javascript as in http://gmap3.net/examples/clustering.html Please suggest any good solution or its a drawback that we can't change existing ratio.

Thanks in advance.