update issue template (#4127)

.github/ISSUE_TEMPLATE.md

@@ -1,7 +1,7 @@
 <!--
 IMPORTANT: Please use the following link to create a new issue:
 
-  https://eleme-issue.surge.sh
+  https://elementui.github.io/issue-generator
 
 If your issue was not created using the app above, it will be closed immediately.
 -->