fix: the date string cannot be converted to Date

2000-10-10 -> Invalid Date, must use 2000/10/10 format in some browers

src/utils/event.js

@@ -63,7 +63,7 @@ function offsetWeek (week, offset) {
 }
 
 export function toDate (val) {
-  return val && new Date(val)
+  return val && new Date(typeof val === 'string' ? val.replace(/-/g, '/') : val)
 }
 
 export function pickMax (a, b) {