updating default chai style to be consistent with docs

According to http://chaijs.com/, assert and expect shouldn't be called as a function. This was breaking my initial Teaspoon installation. I also updated https://github.com/modeset/teaspoon/wiki/Quick-Start-Walkthrough to reflect updated chai expect syntax. Hope that helps!
Merge pull request #157 from tkriplean/patch-1

updating default chai style to be consistent with docs