Clarify computed properties reactive dependencies (vuejs#2044)

Author: Eido95

src/v2/guide/computed.md

@@ -94,7 +94,7 @@ methods: {
 }
 ```
 
-Instead of a computed property, we can define the same function as a method instead. For the end result, the two approaches are indeed exactly the same. However, the difference is that **computed properties are cached based on their dependencies.** A computed property will only re-evaluate when some of its dependencies have changed. This means as long as `message` has not changed, multiple access to the `reversedMessage` computed property will immediately return the previously computed result without having to run the function again.
+Instead of a computed property, we can define the same function as a method instead. For the end result, the two approaches are indeed exactly the same. However, the difference is that **computed properties are cached based on their reactive dependencies.** A computed property will only re-evaluate when some of its reactive dependencies have changed. This means as long as `message` has not changed, multiple access to the `reversedMessage` computed property will immediately return the previously computed result without having to run the function again.
 
 This also means the following computed property will never update, because `Date.now()` is not a reactive dependency: