fix some spell error (#589)

* change normalizePosotion to normalizePosition

* revert flow syntax

Author: yolo2013

src/history/html5.js

@@ -8,7 +8,7 @@ import {
   saveScrollPosition,
   getScrollPosition,
   isValidPosition,
-  normalizePosotion,
+  normalizePosition,
   getElementPosition
 } from '../util/scroll-position'
 
@@ -94,10 +94,10 @@ export class HTML5History extends History {
         if (el) {
           position = getElementPosition(el)
         } else if (isValidPosition(shouldScroll)) {
-          position = normalizePosotion(shouldScroll)
+          position = normalizePosition(shouldScroll)
         }
       } else if (isObject && isValidPosition(shouldScroll)) {
-        position = normalizePosotion(shouldScroll)
+        position = normalizePosition(shouldScroll)
       }
 
       if (position) {

src/util/scroll-position.js

@@ -26,7 +26,7 @@ export function isValidPosition (obj: Object): boolean {
   return isNumber(obj.x) || isNumber(obj.y)
 }
 
-export function normalizePosotion (obj: Object): Object {
+export function normalizePosition (obj: Object): Object {
   return {
     x: isNumber(obj.x) ? obj.x : window.pageXOffset,
     y: isNumber(obj.y) ? obj.y : window.pageYOffset