Correct singular to plural (#842)

* Correct singular to plural

* Slight wording change

Author: zaccharles

docs/en/api/route-object.md

@@ -10,15 +10,15 @@ The route object can be found in multiple places:
 
 - As the return value of calling `router.match(location)`;
 
-- Inside navigation guards as the first and second argument:
+- Inside navigation guards as the first two arguments:
 
   ``` js
   router.beforeEach((to, from, next) => {
     // to and from are both route objects
   })
   ```
 
-- Inside the `scrollBehavior` function as the first and second argument:
+- Inside the `scrollBehavior` function as the first two arguments:
 
   ``` js
   const router = new VueRouter({