Refresh to Travis CI configuration.

This commit updates the Travis Continuous Integration configuration to
make it work again.

I chose a different approach to installing the SDK, that avoid depending
on the order in which things are returned by the tool and breaks each
time something changes (like a new release). Instead use static links to
the SDK components that we need.

Since the continuous build is not reliable enough (or at least I am not
sure it is), also only notify myself of failures.
Use less specific CSS selectors for the default font.

Targetting .question and .answer will override anything set outside of
those, namely .card{}.
Merge pull request #33 from hssm/default-font-selector

Use less specific CSS selectors for the default font.
Merge pull request #31 from flerda/v2.1-travis

Refresh to Travis CI configuration.