No mobs spawning!!!

Put the summary of the bug you're having here
I wanted to make my self some leather armor
What I expected to happen was...:
I would find a cow or at least another mob

What actually happened was...:
No mobs spawned, I walked through my whole map 5 times, but still no mobs!!!

Steps to Reproduce:
1. Create a new world
2. Enter the new world
3. Walk around the world to check if there are any mobs/animals