Configure Travis to run tests in node 0.10.x

Some of the devDependencies doesn't work with node 0.8.x and 0.6.x,
and we'll be running tests in browsers anyway. Developers can be
expected to keep up to date and use modern node environments. There
are no non-dev dependencies that require older node.
Merge pull request #8 from mroderick/configure-travis

Configure Travis to run tests in node 0.10.x