Refactor code to use arrow functions

Author: brummelte

lib/index.js

@@ -1,23 +1,19 @@
 function createSleepPromise(timeout) {
-    return new Promise(function(resolve) {
+    return new Promise(resolve => {
         setTimeout(resolve, timeout);
     });
 }
 
 function sleep(timeout) {
     // Pass value through, if used in a promise chain
     function promiseFunction(value) {
-        return createSleepPromise(timeout).then(function() {
-            return value;
-        });
+        return createSleepPromise(timeout).then(() => value);
     }
 
-    var sleepPromise = createSleepPromise(timeout);
+    const sleepPromise = createSleepPromise(timeout);
 
     // Normal promise
-    promiseFunction.then = function() {
-        return sleepPromise.then.apply(sleepPromise, arguments);
-    };
+    promiseFunction.then = (...args) => sleepPromise.then(...args);
     promiseFunction.catch = Promise.resolve().catch;
 
     return promiseFunction;