Marked int as unsigned to prevent compiler warning.

It should be ok to use an unsigned int here cause it's a loop index based on an NSArray. Personally I would use NSUInteger, this will help when compiling for ARM64. But to stay in line with the rest of the XTrace code I opted not to do so.
Merge pull request #3 from jeroenleenarts/patch-1

Marked int as unsigned to prevent compiler warning.