Fix travis.yml to run with correct Node.js version

This changes the `.travis.yml` to use the correct Node.js version
by using strings as version numbers.

Relevant Travis CI documentation page: http://about.travis-ci.org/docs/user/languages/javascript-with-nodejs/#Choosing-Node-versions-to-test-against

Without using strings to specify the desired versions Travis CI
runs on Node.js 0.1 instead of 0.10.
Merge pull request #42 from mrnugget/patch-1

Fix travis.yml to run with correct Node.js version
Add async save, triggering off existence of callback
Merge pull request #43 from carter-thaxton/master

Add async save method
videocapture read now uses err, im convention
Merge branch 'master' of github.com:peterbraden/node-opencv into beta