Dev 1.0

I think this method should return a value from the dictionary. Then by calling this method, we'll assign the value to self.highScore.
ex.
```
- (NSInteger) getCurrentHighScore{
    NSMutableDictionary *dictionary = [NSMutableDictionary dictionaryWithContentsOfFile:[self filePath]];
    NSInteger currentHighScore = [[dictionary valueForKey:HIGHSCORE_KEY] intValue];

    return currentHighScore;
}
```
Then assign to self.highScore:
```self.highScore = [self getCurrentHighScore];```
:bow: