tls option in DSN not existing

Just a question if not an issue. But I had to append "&tls=true" to the DSN in order to enable secure connection.
Is this an acceptable way?

```go
db, err := sql.Open("mysql", cfg.FormatDSN() + "&tls=true")
if err != nil {
    log.Fatal(err)
}
```

I cannot do it like:
```go
cfg.TLS = tlsConfig
cfg.InterpolateParams = true
cfg.tls = true // no property of this name
```