fixed ColumnMap.Nullable docs
fixed ColumnMap.Nullable docs

jmoiron/modl,outdoorsy/gorp,losinggeneration/gorp,kevinc0825/gorm,coopernurse/gorp,mousesun/gorp,japettyjohn/modl,rickb777/gorp-old2,go-gorp/gorp,mousesun/gorp,xiaoenai/gorp,xiaoenai/gorp,kimxilxyong/gorp,cortex/gorp,d-g-laptev/gorp,coopernurse/gorp,d-g-laptev/gorp,evenco/gorp,yp-engineering/gorp,kimxilxyong/gorp,kevinc0825/gorm,rickb777/gorp-old2,outdoorsy/gorp,evenco/gorp,japettyjohn/modl,GeertJohan/gorp,jmoiron/modl,yp-engineering/gorp,go-gorp/gorp,losinggeneration/gorp,gabelula/gorp,gabelula/gorp,cortex/gorp,GeertJohan/gorp