Fixed #10 NPE with ScalikeJDBC 1.6.11 - 1.7.0

Since ScalikeJDBC's WrappedResultSet has been changed internally in 1.6.11, ScalikeJDBC-Async's AsyncResultSet#long(Int) and so on throw NPE when working with it.
version 0.3.1
Merge branch 'release/0.3.1'