Added SWIFT_VERSION to XCode project

[mathieumg]

Without this, the pod install fails on CocoaPods 1.6.0 with the following error:

$ pod install
Analyzing dependencies
Pre-downloading: `iOSPhotoEditor` from `https://github.com/prscX/photo-editor`
Downloading dependencies
Installing iOSPhotoEditor (0.5)
[!] Unable to determine Swift version for the following pods:

- `iOSPhotoEditor` does not specify a Swift version and none of the targets (`RNPhotoEditor`) integrating it have the `SWIFT_VERSION` attribute set. Please contact the author or set the `SWIFT_VERSION` attribute in at least one of the targets that integrate this pod.

Even though it do is specified therein. This works around that.

[prscX]

Thanks @mathieumg for sharing the PR.

I have merged the same.

Thanks
</ Pranav >

[mathieumg]

Thanks @prscX for the responsiveness! 😎