Fix reference to 'db' var

[eliben]

In the rest of the example db is used, not Db. Moreover, I think that a simple example here could help clarify the terminology, because it gets a bit murky between db (object of type DB) and tx (object of type Tx). Something like:

// Create an object of type Tx
tx, err := db.Begin()
...

[xaprb]

@eliben I'd like to add you as a collaborator, is that okay? You have good judgment and you should just make the changes you see fit. Do you have two-factor auth enabled on GitHub? it's part of our corporate security policy.

[eliben]

@eliben I'd like to add you as a collaborator, is that okay? You have good judgment and you should just make the changes you see fit. Do you have two-factor auth enabled on GitHub? it's part of our corporate security policy.

I don't think that will be necessary. I was just reading through the tutorial and I'm done now :-)

Thanks for publishing it