Build: Uses different strategy to test bins status

Only 90% of the test should pass.

Related: https://github.com/sass/node-sass/issues/487#issuecomment-60902761 and https://github.com/sass/node-sass/issues/490.

/cc @andrew, @nschonni, @keithamus, @kevva
Rather than have more linting in the test suite, we need something like https://codeclimate.com/ or http://houndci.com to encourage following the styleguide.