SVG mime-type mapping is incorrect

[dustinconrad]

I am no expert, but I believe the correct mime-type for SVG is image/svg+xml.

In Http.kt it is image/svg which I don't believe is a valid mime-type. I think this results in generating tf files with as content-type of image/svg instead of image/svg+xml.

EDIT: just looked at PRs, I think #98 actually fixes this, among other things