[doc] Update busted version mentioned in docs (#9078)

doc/Unit_tests.md

@@ -2,12 +2,12 @@
 
 Unit tests are automatically performed using [busted](http://olivinelabs.com/busted/). It depends on `luarocks`.
 
-To grab busted, install the same version [as used in the automated tests](https://github.com/koreader/koreader/blob/master/.ci/install.sh). At the time of writing that is 2.0.rc12-1:
+To grab busted, install the same version [as used in the automated tests](https://github.com/koreader/koreader/blob/master/.ci/install.sh). At the time of writing that is 2.0.0-1:
 ```bash
 mkdir $HOME/.luarocks
 cp /etc/luarocks/config.lua $HOME/.luarocks/config.lua
 echo "wrap_bin_scripts = false" >> $HOME/.luarocks/config.lua
-luarocks --local install busted 2.0.rc12-1
+luarocks --local install busted 2.0.0-1
 ```
 Then you can set up the environment variables with `./kodev activate`.