Support target="_blank" for <router-link> (#830)

* Support `target="_blank"` for `<router-link>`

* Fix trailing spaces

* small fix

* yet another small fix

* hopefully final fix...

* fix implementation

Author: fnlctrl

src/components/link.js

@@ -50,6 +50,11 @@ export default {
         // don't redirect on right click
         /* istanbul ignore if */
         if (e.button !== 0) return
+        // don't redirect if `target="_blank"`
+        /* istanbul ignore if */
+        const target = e.target.getAttribute('target')
+        if (/\b_blank\b/i.test(target)) return
+
         e.preventDefault()
         if (this.replace) {
           router.replace(to)