Using 'stringWithString:' with a literal is redundant

On line 360 I get the following compiler warning regarding NSString:

```
TBXML.m:360:25: Using 'stringWithString:' with a literal is redundant
```

Could you please fix this line from 

``` Objective-C
value = [NSString stringWithString:@""];
```

to 

``` Objective-C
value = @"";
```

Thanks!
