Fix image creator format

Hi, I think i've fixed two bugs on the number to text conversion code:

1. The test  ```testNumberToTextConversion``` was expecting the method output to be equal to itself.
1. The ```$dimensions``` array in ```ÍmageCreator::transformNumberToReadableFormat``` caused a failure when run on a 32bit machine because of the long array keys. Mabye this is what @leopro experienced before commenting the billons line.