style: clear default login credentials and replace demo tip with poem

src/components/login-form/login-form.vue

@@ -40,8 +40,8 @@ export default {
     return {
       loading: false,
       form: {
-        username: 'admin',
+        username: '',
-        password: '123456'
+        password: ''
       }
     }
   },

src/view/login/login.less

@@ -20,8 +20,9 @@
             padding: 10px 0 0;
         }
         .login-tip{
-            font-size: 10px;
+            font-size: 12px;
             text-align: center;
+            letter-spacing: 2px;
             color: #c3c3c3;
         }
     }

src/view/login/login.vue

@@ -26,7 +26,7 @@
         <Card icon="log-in" title="欢迎登录" :bordered="false">
           <div class="form-con">
             <login-form ref="loginForm" @on-success-valid="handleSubmit"></login-form>
-            <p class="login-tip">演示使用，仅供学习交流使用</p>
+            <p class="login-tip">海阔凭鱼跃，天高任鸟飞</p>
           </div>
         </Card>
       </div>