Update stgvis.Rmd

I changed the gvisGeoMap statement to gvisGeoChart, as they don't require Flash. Further the Google geo charts understand that Berlin is not part of Brandenburg. Unfortunately, geo charts don't recognise Brandenburg as a province either, hence the codes become handy again.
The German state name mapping are available via a CRAN package, thus you don't have to download them from Wikipedia. Finally, I added some number formatting to the option setting.
Merge pull request #19 from mages/patch-1

Update stgvis.Rmd