Fix script to install luadocumentor

78577b255d19a1f4f4f539662e00357936b73c33 is a part of
https://gitlab.com/ptmikheev/openmw-luadocumentor.git repo. Before doing
checkout need to change the directory.

docs/source/install_luadocumentor_in_docker.sh

@@ -30,8 +30,8 @@ PATH=$PATH:~/luarocks/bin
 
 echo "Install openmwluadocumentor"
 git clone https://gitlab.com/ptmikheev/openmw-luadocumentor.git
-git checkout 78577b255d19a1f4f4f539662e00357936b73c33
 cd openmw-luadocumentor
+git checkout 78577b255d19a1f4f4f539662e00357936b73c33
 luarocks make luarocks/openmwluadocumentor-0.2.0-1.rockspec
 cd ~
 rm -r openmw-luadocumentor