String format for tabsToAdd array

[dstmartin]

I was getting an error when running gulp patternlab:build. It appears the issue is that the strings need a double quote (") as opposed to a single quote (').

In other words, "tabsToAdd": ['scss'] needs to be changed to "tabsToAdd": ["scss"]. Doing this allowed me to perform a build.

[c42705]

@bmuenzenmeyer please update README.md with this update, I ran into the same issue.

[juanfernandes]

i have created a pull request to fix this.

#27