added the link to funcitonal components (#1926)

Author: amadeann

Diff for: src/v2/guide/transitions.md

@@ -1479,7 +1479,7 @@ Vue.component('my-special-transition', {
 })
 ```
 
-And functional components are especially well-suited to this task:
+And [functional components](render-function.html#Functional-Components) are especially well-suited to this task:
 
 ``` js
 Vue.component('my-special-transition', {