fix doc typos (#1137)

examples/docs/en-US/installation.md

@@ -36,7 +36,7 @@ If you are using CDN, a hello-world page is easy with Element. [Online Demo](htt
     </el-dialog>
   </div>
 </body>
-  <!-- import Vue before Mint UI -->
+  <!-- import Vue before Element -->
   <script src="https://unpkg.com/vue/dist/vue.js"></script>
   <!-- import JavaScript -->
   <script src="https://unpkg.com/element-ui/lib/index.js"></script>

examples/docs/en-US/quickstart.md

@@ -142,7 +142,7 @@ import ElementUI from 'element-ui'
 import 'element-ui/lib/theme-default/index.css'
 import App from './App.vue'
 
-Vue.use(MintUI)
+Vue.use(ElementUI)
 
 new Vue({
   el: '#app',