change reactive method to reactive function (#1199)

Author: Yukon123

src/api/refs-api.md

@@ -16,7 +16,7 @@ count.value++
 console.log(count.value) // 1
 ```
 
-If an object is assigned as a ref's value, the object is made deeply reactive by the [reactive](./basic-reactivity.html#reactive) method.
+If an object is assigned as a ref's value, the object is made deeply reactive by the [reactive](./basic-reactivity.html#reactive) function.
 
 **Typing:**