[CopyResourcesScript] FIX xcassets not compatible with Xcode < 5.0.0.

Added additional `if-statement` to check if Xcode 5 is installed. 

`xcassets` were introduced in that version and if you try compile Xcode 5 project on Xcode 4.6 (when testing on Travis as Travis has not yet been updated with Xcode 5), the entire test fails due to build failure:

```
Run custom shell script 'Copy Pods Resources'
...
xargs: actool: No such file or directory
```