Insert() not works for postgresql

[LiveLikeLastDay]

I think that last_insert_rowid is for SQL server, postgresql should use LASTVAL();

Exception Details:
{Npgsql.PostgresException: 42601: syntax error at or near "select"
   at Npgsql.NpgsqlConnector.DoReadMessage(DataRowLoadingMode dataRowLoadingMode, Boolean isPrependedMessage)
   at Npgsql.NpgsqlConnector.ReadMessageWithPrepended(DataRowLoadingMode dataRowLoadingMode)
   at Npgsql.NpgsqlConnector.ReadExpecting[T]()
   at Npgsql.NpgsqlDataReader.NextResultInternal()
   at Npgsql.NpgsqlDataReader.NextResult()
   at Npgsql.NpgsqlCommand.Execute(CommandBehavior behavior)
   at Npgsql.NpgsqlCommand.ExecuteDbDataReaderInternal(CommandBehavior behavior)
   at Dapper.SqlMapper.ExecuteReaderWithFlagsFallback(IDbCommand cmd, Boolean wasClosed, CommandBehavior behavior)
   at Dapper.SqlMapper.<QueryImpl>d__1241.MoveNext()
   at System.Collections.Generic.List1..ctor(IEnumerable1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable1 source)
   at Dapper.SqlMapper.Query[T](IDbConnection cnn, String sql, Object param, IDbTransaction transaction, Boolean buffered, Nullable1 commandTimeout, Nullable`1 commandType)
   at Dommel.DommelMapper.Insert[TEntity](IDbConnection connection, TEntity entity, IDbTransaction transaction)
   at xxxx.Controllers.Api.BaseController.Create[T](T item) 
....
   at lambda_method(Closure , Object , Object[] )
   at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeActionFilterAsync>d__28.MoveNext()}

[henkmollema]

Would you like to send a PR? :smile:

[henkmollema]

By the way, isn't using RETURNING even better? http://stackoverflow.com/a/2944481/1823494

[LiveLikeLastDay]

Never done pull request before, but I'd like to have a try.