Fix Link component to guard the event if alt key is pressed (#1484)

Author: yuheiy

src/components/link.js

@@ -105,7 +105,7 @@ export default {
 
 function guardEvent (e) {
   // don't redirect with control keys
-  if (e.metaKey || e.ctrlKey || e.shiftKey) return
+  if (e.metaKey || e.altKey || e.ctrlKey || e.shiftKey) return
   // don't redirect when preventDefault called
   if (e.defaultPrevented) return
   // don't redirect on right click