Switch to Microsoft MSSQL to fix init() driver Registration conflicts

[jrapoport]

The denisenkom go-mssqldb library is outdated and causes a double-registration panic with other libraries that use the newer Microsoft one like Gorm:

func init() {
	registry.Register("mssql", func() gnomock.Preset { return &P{} })
}

Swapped github.com/denisenkom/go-mssqldb for github.com/microsoft/go-mssqldb

(microsoft version looks like a fork of denisenkom and works as a drop in replacement -- tests pass)

[orlangure]

Thank you for fixing this!

[jrapoport]

my pleasure!