fix(input-groups): added themeable for the **solo** prop
fix(input-groups): added themeable for the **solo** prop

fixes #2705

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