Uint support

[walnuts1018]

fix #317

Currently, uint is cast to int64, causing overflow in some values and generating unexpected queries.

Example: (from #317)

package main

import (
	"github.com/doug-martin/goqu/v9"
	_ "github.com/doug-martin/goqu/v9/dialect/mysql" // needed for mysql dialect of query builder
)

type Sample struct {
	Uint64 uint64 `db:"uint_64"`
}

func main() {
	sample := Sample{
		Uint64: 11169823557460058355,
	}
	dialect := goqu.Dialect("mysql")
	query := dialect.Insert("tableName").Rows(sample)
	sql, _, _:= query.ToSQL()
	print(sql)
}

expect: INSERT INTO tableName (uint_64) VALUES (11169823557460058355)
result: INSERT INTO tableName (uint_64) VALUES (-7276920516249493261)

This PR solves the problem by adding a case for uint.

[walnuts1018]

@funkyshu Review please.