Fix error building node-sass on travis

Used this as a blueprint travis.yml: https://github.com/sass/node-sass/blob/master/.travis.yml
More info: https://github.com/sass/node-sass/issues/497#issuecomment-62552565
And here: https://github.com/sass/node-sass/issues/490
avoid use of Function.bind
Merge pull request #10 from bantic/fix-tests

Fix error building node-sass on travis