[maven-release-plugin] prepare release RoaringBitmap-0.6.4
[maven-release-plugin] prepare release RoaringBitmap-0.6.4

lemire/RoaringBitmap,okrische/RoaringBitmap,RoaringBitmap/RoaringBitmap,RoaringBitmap/RoaringBitmap,lemire/RoaringBitmap,okrische/RoaringBitmap,lemire/RoaringBitmap,RoaringBitmap/RoaringBitmap,lemire/RoaringBitmap,okrische/RoaringBitmap,RoaringBitmap/RoaringBitmap