Install Subversion (SVN) as follows:
sudo apt-get install subversion
This command exports the GitHub PROJECT folder and subfolders and to DEST
svn export https://github.com/USER/PROJECT/trunk/PATH DEST
Suffix the PROJECT folder with /trunk and append the folder /PATH you wish to download. If the DEST folder does not exist it is automatically created.
For example the following command copies Tutsplus 30-days-to-jquery/lessons folder to lessons folder on the local drive:
svn export https://github.com/tutsplus/30-days-to-jquery/trunk/lessons lessons