Provide viewBox for svg wrapper element in stack mode

[rqelibari]

When using stack mode, the most outer svg tag in the result file does not contain a viewBox attribute.
This causes an undesired rendering in Safari (8.0.5), Chrome (42.0.2311.90) and Firefox (37.0.1) (I didn't test IE), when the svg file is included via fragment identifiers in an object tag:

<object data="/path/to/sprite.stack.svg#terminal" type="image/svg+xml"></object>

And here a screenshot of Safari:

See that <object> does not fill whole <div> by width? Even style="width: 100% on <object>-Tag wouldn't change that.
The solution I've found out till now, is to include the viewBox attribute in the most outer svg of the file in the form:

<?xml ... ?><svg xmlns="..." xmlns:xlink:="..." viewBox="0 0 maxWidth maxHeight">...</svg>

maxWidth is hereby the maximal width of all included svgs. Same applies for maxHeight.
Again a screenshot in Safari after applying this rule:

I build a quick fix for that, modifying: lib/svg-sprite/mode/stack.js. Adding the following lines to the _buildSVG function will solve that problem:

    svg = new SVGSprite(...

    var maxWidth = 0, maxHeight=0;
    _.each(this.data.shapes, function(obj){
        if (obj.width.outer > maxWidth) maxWidth = obj.width.outer;
        if (obj.height.outer > maxHeight) maxHeight = obj.height.outer;
    });
    svg.rootAttributes.viewBox = "0 0 " + maxWidth + " " + maxHeight;

    return svg.toFile(...

Attention:
This is a quick fix. I didn't analyze the code base, so I don't know if this is the right place to put this or if there exists already an option for this. That's also the reason why I didn't provide a pull request.
However I can provide one as soon as I get feedback, if this is the right place and this fix is needed.

[jkphl]

Hey @rqelibari,

thanks for reporting this. To be honest, I probably never really checked using the stack sprite in conjunction with an <object> element. The only reason for skipping the viewBox attribute was to save some bytes — I can't think of any downsides. I'll incorporate it as you suggested. :)

Cheers,
Joschi