Add Contributors alias for Contributor

Because the contract is named `Contributors` we alias to `Contributor` which will become the new contract name if we manage to change it.

lib/kredits.js

@@ -63,6 +63,11 @@ class Kredits {
     return this.contractFor('contributors');
   }
 
+  get Contributors() {
+    console.log('Contributors is deprecated use Contributor instead');
+    return this.Contributor;
+  }
+
   get Operator() {
     return this.contractFor('operator');
   }