docs: use local copy of bit logo

Author: posva

docs/.vuepress/components/Bit.vue

@@ -2,7 +2,7 @@
   <p class="bit-sponsor">
     <a href="https://www.bitsrc.io/?utm_source=vue&utm_medium=vue&utm_campaign=vue&utm_term=vue&utm_content=vue" target="_blank">
       <span>This project is sponsored by</span>
-      <img alt="bit" src="https://raw.githubusercontent.com/vuejs/vuejs.org/master/themes/vue/source/images/bit.png">
+      <img alt="bit" src="/bit-wide.png">
     </a>
   </p>
 </template>