support floating point values in the viewBox property

[cedrics]

I got an SVG icon from our designers and the viewBox property had a floating-point value in it, so the property was not assigned. Small fix for that 😸

[adrianmroz]

I'm wondering if we should match anything specific there? We wan't to pick viewBox attribute and pass it further.

By the way original code looks weird. It matches viewBox, strips <svg> from string but only if it has space in it (ergo any attribute). Could you clean up this code a bit, since you're modifying it? Maybe we should createDocumentFragment with svg string content and read viewBox using DOM API and take innerText instead of stripping string with regexes?