ESLint one-var, no-var rules (#3239)

* fixed issues for eslint one-var and no-var rules

Co-authored-by: Joshi <simplyrender@gmail.com>
Co-authored-by: Andrew Henry <akhenry@gmail.com>

src/api/composition/CompositionCollection.js

@@ -128,7 +128,7 @@ define([
             throw new Error('Event not supported by composition: ' + event);
         }
 
-        var index = this.listeners[event].findIndex(l => {
+        const index = this.listeners[event].findIndex(l => {
             return l.callback === callback && l.context === context;
         });