remove :is attribute even when component is cached (fixes #2666) (#2672)

Author: GuillaumeLeclerc

src/directives/internal/component.js

@@ -56,6 +56,7 @@ export default {
       // cached, when the component is used elsewhere this attribute
       // will remain at link time.
       this.el.removeAttribute('is')
+      this.el.removeAttribute(':is')
       // remove ref, same as above
       if (this.descriptor.ref) {
         this.el.removeAttribute('v-ref:' + hyphenate(this.descriptor.ref))