Simplify the code by using `p-finally`

Closes #1

index.js

@@ -1,4 +1,5 @@
 'use strict';
+const pFinally = require('p-finally');
 
 class TimeoutError extends Error {
 	constructor(message) {
@@ -24,14 +25,10 @@ module.exports = (promise, ms, fallback) => new Promise((resolve, reject) => {
 		reject(err);
 	}, ms);
 
-	promise.then(
-		val => {
+	pFinally(
+		promise.then(resolve, reject),
+		() => {
 			clearTimeout(timer);
-			resolve(val);
-		},
-		err => {
-			clearTimeout(timer);
-			reject(err);
 		}
 	);
 });

package.json

@@ -31,6 +31,9 @@
     "cancel",
     "bluebird"
   ],
+  "dependencies": {
+    "p-finally": "^1.0.0"
+  },
   "devDependencies": {
     "ava": "*",
     "delay": "^1.3.1",