feat: make it possible to crop transaprent images on ios (#39)

Author: Trancever

ios/RNCImageEditor.m

@@ -74,7 +74,7 @@ @implementation RNCImageEditor
     // Store image
     NSString *path = [RNCFileSystem generatePathInDirectory:[[RNCFileSystem cacheDirectoryPath] stringByAppendingPathComponent:@"ReactNative_cropped_image_"] withExtension:@".jpg"];
 
-    NSData *imageData = UIImageJPEGRepresentation(croppedImage, 1);
+    NSData *imageData = UIImagePNGRepresentation(croppedImage);
     NSError *writeError;
     NSString *uri = [RNCImageUtils writeImage:imageData toPath:path error:&writeError];