README update

Author: Gilles Grousset

README.md

@@ -118,7 +118,7 @@ Otherwise, run the ```run-sonar-swift.sh``` script from your Xcode project root
 - [xcpretty](https://github.com/supermarin/xcpretty) (see instructions below)
 - [SwiftLint](https://github.com/realm/SwiftLint) ([HomeBrew](http://brew.sh) installed and ```brew install swiftlint```). Version 0.3.0 or above.
 - [Tailor](https://github.com/sleekbyte/tailor) ([HomeBrew](http://brew.sh) installed and ```brew install tailor```). Version 0.11.1 or above.
-- [slather](https://github.com/SlatherOrg/slather) (```gem install slather```). Version 2.1.0 or above.
+- [slather](https://github.com/SlatherOrg/slather) (```gem install slather```). Version 2.1.0 or above (2.4 since Xcode 8.3).
 - [lizard](https://github.com/terryyin/lizard) ([PIP](https://pip.pypa.io/en/stable/installing/) installed and ```sudo pip install lizard```)
 
 ### Installation of xcpretty with JUnit reports fix