Log Message:
Updated ruby23-squib to 0.13.3.

## v0.13.3 / 2017-07-15

Bugs:
* Fix `undefined method [] for nil:NilClass` error on `svg` (was a regression \ 
error in librsvg that we worked around.)
* Bump dependencies to latest stable versions. Pango et al. to 3.1.7 and Cairo \ 
to 1.15.9. This fixes some compatibility issues.