Update README.md

I have found the pronunciation of GUI of the original version sounds like the Chinese pronunciation of 贵, so I checked WIKI for it. 
'The graphical user interface (GUI /ɡuːiː/), is a type of user interface that...'  quoted from wiki.
https://en.wikipedia.org/wiki/Graphical_user_interface

README.md

@@ -29,7 +29,7 @@
 | fedora [🔊](http://dict.youdao.com/dictvoice?audio=fedora&type=1) | ✅ [fɪ'dɔːrə]| ❌ ['fedərə] |
 | Git [🔊](http://dict.youdao.com/dictvoice?audio=git&type=1) | ✅ [ɡɪt] | ❌ [dʒɪt; jɪt] |
 | GNU [🔊](https://upload.wikimedia.org/wikipedia/commons/2/24/En-gnu.ogg) | ✅ [gnu:] | |
-| GUI [🔊](http://dict.youdao.com/dictvoice?audio=GUI&type=1) | ✅ [ˈɡui] | |
+| GUI [🔊](https://n1audio.hjfile.cn/newylk/2017/08/30/ac56985ceeaf0f56fe15d53cda080d01.mp3) | ✅ [ˈɡu:i] | |
 | Haskell [🔊](http://dict.youdao.com/dictvoice?audio=haskell&type=1) | ✅ [ˈhæskəl] | ❌ [hæˈskəl] |
 | height [🔊](http://dict.youdao.com/dictvoice?audio=height&type=1) | ✅ [haɪt] | ❌ [heɪt] |
 | hidden [🔊](http://dict.youdao.com/dictvoice?audio=hidden&type=1) | ✅ ['hɪdn] | ❌ ['haɪdn] |