Change teams score data type to integer

Somewhere, somehow, team score got changed to be a string instead of an integer. This was resulting in the error when trying to score a goal:

```ruby
TypeError at /games/3/score
===========================

> no implicit conversion of Fixnum into String

app/models/score.rb, line 19
----------------------------
   14     #
   15     def add_score
   16       transaction do
   17         self.player.points = self.player.points + 1
   18         if self.player.save
>  19           self.player.team.score = self.player.team.score + 1
   20           self.player.team.save
   21         end
   22         self.player.inc_score_stats
   23       end
   24     end
```

This change adds a new migration that updates the team.score type from string to integer.