change contributors link to amber-smalltalk (fix #968)

README.md

@@ -1,7 +1,7 @@
 Amber [![Travis CI Status](https://secure.travis-ci.org/amber-smalltalk/amber.png)](https://travis-ci.org/#!/amber-smalltalk/amber)
 =====
 
-By Nicolas Petton <petton.nicolas@gmail.com> and [Amber contributors](https://github.com/NicolasPetton/amber/contributors)
+By Nicolas Petton <petton.nicolas@gmail.com> and [Amber contributors](https://github.com/amber-smalltalk/amber/contributors)
 
 Amber is an implementation of the Smalltalk language that runs on top of the JavaScript runtime. It is designed to make client-side development faster and easier.