QBtnDropdown not display correct with full-width classname .

[luozhihua]

Describe the bug
QBtnDropdown not display correct with full-width classname .

Codepen/jsFiddle/Codesandbox (required)
https://codepen.io/colinluo/pen/MWKGvRz?editors=1010

To Reproduce
Steps to reproduce the behavior:

1. Add classname 'full-width' to QBtnDropdown component
2. View the QBtnDropdown UI in browser
3. See error

Expected behavior
QBtnDropdown display correct with full-width classname

Solution
Add following css code can fix it:

.q-btn-dropdown.full-width .q-btn-dropdown--current{
  flex: 1;
}

Screenshots
If applicable, add screenshots to help explain your problem.

Platform (please complete the following information):

➜ quasar info

Operating System - Darwin(19.6.0) - darwin/x64
NodeJs - 14.4.0

Global packages
  NPM - 6.14.5
  yarn - Not installed
  @quasar/cli - 1.1.0
  cordova - You have been opted out of telemetry. To change this, run: cordova telemetry on.
9.0.0 (cordova-lib@9.0.1)

Important local packages
  quasar - 1.12.8 -- Build high-performance VueJS user interfaces (SPA, PWA, SSR, Mobile and Desktop) in record time
  @quasar/app - 2.0.1 -- Quasar Framework local CLI
  @quasar/extras - 1.8.2 -- Quasar Framework fonts, icons and animations
  eslint-plugin-quasar - 1.0.0 -- Official ESLint plugin for Quasar
  vue - 2.6.11 -- Reactive, component-oriented view layer for modern web interfaces.
  vue-router - 3.2.0 -- Official router for Vue.js 2
  vuex - 3.4.0 -- state management for Vue.js
  electron - 9.0.5 -- Build cross platform desktop apps with JavaScript, HTML, and CSS
  electron-packager - Not installed
  electron-builder - Not installed
  @capacitor/core - Not installed
  @capacitor/cli - Not installed
  @capacitor/android - Not installed
  @capacitor/ios - Not installed
  @babel/core - 7.10.4 -- Babel compiler core.
  webpack - 4.43.0 -- Packs CommonJs/AMD modules for the browser. Allows to split your codebase into multiple bundles, which can be loaded on demand. Support loaders to preprocess files, i.e. json, jsx, es7, css, less, ... and your custom stuff.
  webpack-dev-server - 3.11.0 -- Serves a webpack app. Updates the browser on changes.
  workbox-webpack-plugin - 5.1.3 -- A plugin for your Webpack build process, helping you generate a manifest of local files that workbox-sw should precache.
  register-service-worker - 1.7.1 -- Script for registering service worker, with hooks
  typescript - 3.9.6 -- TypeScript is a language for application scale JavaScript development

Quasar App Extensions
  @quasar/quasar-app-extension-dotenv - 1.0.3 -- Load .env variables into your quasar project
  @quasar/quasar-app-extension-typescript - 1.0.2 -- A Quasar CLI Extension

Additional context
Add any other context about the problem here.

[webnoob]

Will be available in 1.12.9