explorercanvas: Bump version and change site

Google Code is a closing forge, libass has already made the move to
Github.

This package has no release yet, so we are using a commit.
Since the tarball is generated by Github, a hash is useless here.

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>