nuget: Specify WP8 dep on sqlite-net-wp8
nuget: Specify WP8 dep on sqlite-net-wp8

kreuzhofer/SQLite.Net-PCL,caseydedore/SQLite.Net-PCL,molinch/SQLite.Net-PCL,fernandovm/SQLite.Net-PCL,TiendaNube/SQLite.Net-PCL,oysteinkrog/SQLite.Net-PCL,mattleibow/SQLite.Net-PCL