Modify White marker background-position

[ghybs]

Hi,
First of all: thank you for the awesome plugin!

In the CSS file, the background-position for white marker is off by 2 pixels:
.awesome-marker-icon-white {
background-position: -574px 0;
}
Should be instead:
.awesome-marker-icon-white {
background-position: -576px 0;
}

Interestingly, the background-position for the black marker is also off by 2 pixels compared to the 36 pixels step, but it renders fine. So it is probably misplaced in the sprite image, and the background-position corrects this difference.