title: use apt-get update E: Failed to fetch http://...... File has unexpected size
body: <pre><code>E: Failed to fetch http://mirrors.kali.com/kali/dists/kali-rolling/main/binary-i386/Packages.gz  File has unexpected size (15320738 != 15317336). Mirror sync in progress? [IP: 111.11.111.111 80]
     Hashes of expected file:
      - Filesize:15317336 [weak]
      - SHA256:c4762e83455984f8d3fb54f6f42836808b8c891ba117661b61240bc5774d2e02
      - SHA1:fdebd56e7541e6f88d7910988ef694d3c409e21d [weak]
      - MD5Sum:51400b889af8677132f31d56f266bf22 [weak]
     Release file created at: Fri, 06 Oct 2017 06:55:45 +0000
  E: Some index files failed to download. They have been ignored, or old ones used instead.
  </code></pre>
  
  <p>this is the error page.How to deal with this problem？</p>