fix: only setupScroll when support pushState due to possible fallback: false (#1835)

* fix #1834

* judge supportsPushState before setupScroll

* expectScroll -> supportsScroll

Author: JounQin

src/history/html5.js

@@ -5,15 +5,16 @@ import { History } from './base'
 import { cleanPath } from '../util/path'
 import { START } from '../util/route'
 import { setupScroll, handleScroll } from '../util/scroll'
-import { pushState, replaceState } from '../util/push-state'
+import { pushState, replaceState, supportsPushState } from '../util/push-state'
 
 export class HTML5History extends History {
   constructor (router: Router, base: ?string) {
     super(router, base)
 
     const expectScroll = router.options.scrollBehavior
+    const supportsScroll = supportsPushState && expectScroll
 
-    if (expectScroll) {
+    if (supportsScroll) {
       setupScroll()
     }
 
@@ -29,7 +30,7 @@ export class HTML5History extends History {
       }
 
       this.transitionTo(location, route => {
-        if (expectScroll) {
+        if (supportsScroll) {
           handleScroll(router, route, current, true)
         }
       })