enh(v-form): listen to hasError instead of valid
enh(v-form): listen to hasError instead of valid

this allows v-form to pick up on manual error messages and the error prop

closes #2519

Phlow2001/vuetify,vuetifyjs/vuetify,Webifi/vuetify,Webifi/vuetify,Phlow2001/vuetify,Phlow2001/vuetify,vuetifyjs/vuetify,Webifi/vuetify,vuetifyjs/vuetify,vuetifyjs/vuetify,Phlow2001/vuetify