chore: update sponsor image

Author: yyx990803

BACKERS.md

@@ -21,7 +21,7 @@ Funds donated via Patreon go directly to support Evan You's full-time work on Vu
     <img width="260px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/stdlib.png">
   </a>
 </p>
-  
+
 <!--special end-->
 
 <h2 align="center">Platinum via Patreon</h2>
@@ -221,7 +221,7 @@ Funds donated via Patreon go directly to support Evan You's full-time work on Vu
       </td>
       <td align="center" valign="middle">
         <a href="https://unicorn.io/" target="_blank">
-          <img width="148px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/unicorn_io.svg">
+          <img width="148px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/unicorn_io.png">
         </a>
       </td>
       <td align="center" valign="middle">

README.md

@@ -31,7 +31,7 @@ Funds donated via Patreon go directly to support Evan You's full-time work on Vu
     <img width="260px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/stdlib.png">
   </a>
 </p>
-  
+
 <!--special end-->
 
 <h3 align="center">Platinum Sponsors</h3>
@@ -226,7 +226,7 @@ Funds donated via Patreon go directly to support Evan You's full-time work on Vu
       </td>
       <td align="center" valign="middle">
         <a href="https://unicorn.io/" target="_blank">
-          <img width="148px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/unicorn_io.svg">
+          <img width="148px" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/unicorn_io.png">
         </a>
       </td>
       <td align="center" valign="middle">