Update image-modification-block.md (TextureGroup#474)

* Update image-modification-block.md

Just some minor proposals for improvements:
- Removed white spaces, which caused the first line in the image modification block to be shown a bit "messy"
- Using the Null coalescing operator in the following line

* Update image-modification-block.md

Now, with the second change as well.

docs/_docs/image-modification-block.md

@@ -17,10 +17,10 @@ By assigning an `imageModificationBlock` to your imageNode, you can define a set
 <pre lang="objc" class="objcCode">
 _backgroundImageNode.imageModificationBlock = ^(UIImage *image) {
 	UIImage *newImage = [image applyBlurWithRadius:30
-										 tintColor:[UIColor colorWithWhite:0.5 alpha:0.3]
-							 saturationDeltaFactor:1.8
-							 			 maskImage:nil];
-	return newImage ? newImage : image;
+		tintColor:[UIColor colorWithWhite:0.5 alpha:0.3]
+		saturationDeltaFactor:1.8
+		maskImage:nil];
+	return newImage ?: image;
 };
 
 //some time later...