blue and green colors were swapped

While playing with a brand new 60-pixel Adafruit DotStar strip with the [Spark Core DotStar library](https://community.spark.io/t/adafruit-dotstar-spi-led-strip-library-ported/8999) I noticed the Blue and Green colors were swapped.  These changes correct that issue.  I will update the Spark Core library after confirmation of this issue ;-)  Thanks!