Fix typo in visits form which causes button to miss its text

[dfuenzalida]

This PR fixes a typo in the text of the submit button of the visits form causing the label of the button to be missing.

Validation

Before:

$ curl -s http://localhost:8080/owners/6/pets/8/visits/new | grep submit
        <button class="btn btn-primary" type="submit"></button>

After (note the "Add Visit" text):

$ curl -s http://localhost:8080/owners/6/pets/8/visits/new | grep submit
        <button class="btn btn-primary" type="submit">Add Visit</button>

[dsyer]

LGTM. You need to sign the commit though.

[dfuenzalida]

LGTM. You need to sign the commit though.

Hi @dsyer, thanks for reviewing. I've updated the commit to include the sign-off.