Pin io.js version to v2.5.0 in .travis.yml for now
Pin io.js version to v2.5.0 in .travis.yml for now

Contextify won't build on io.js v3.0 currently. Until that is fixed,
we'll test on v2.5.0 so that our tests pass.

yjerem/pencil-tracer,yjerem/pencil-tracer