How to make game fit screen on Unity

I'm developing a game, and in Unity I've set the resolution to 1280x800. When I export to Android, I expect it to adjust to the screen (adding black bars if necessary) but it isn't the case.

This is how it looks like on a Nexus 4:

And on Nexus 5:

How can I make it so that it looks the same everywhere? (having black bars if necessary as I said before).