Log Message:
librsvg: update to 2.48.1.

Version 2.48.1

- #129 - Fix baseline-shift for simple subscripts/superscripts and
  absolute offsets.  This should fix a lot of Wikimedia images with
  formulas.

- #548 - Support images with data: URLs that don't have a MIME-type.
  This fixes some Open Clip Art images generated by old versions
  of Adobe Illustrator.

- Fix build of the test suite on Windows (Chun-wei Fan).

- Support running the rsvg_internals tests on Windows (Chun-wei Fan).