fix compile error:
collection.scala:159: too many arguments for constructor RenameCollection: (name: String, target: String, dropTarget: Boolean)reactivemongo.core.commands.RenameCollection
[error]   def rename(to: String, dropExisting: Boolean = false)(implicit ec: ExecutionContext): Future[Boolean] = db.command(new RenameCollection(db.name + "." + name, db.name + "." + to, to, dropExisting))
Merge pull request #122 from imikushin/fix-too-many-args-err

fix compile error