Remove Travis CI conf.

Couldn't get it working; may try again later.

Revert "Add rake to Gemfile for Travis CI"

This reverts commit 4fcaffa493cd2fb2e0c82b4edc0a15af728b7f1e.

Revert "Travis CI config."

This reverts commit b786a836b6e56e820a120b8c9fcd838220b8d30d.