Update setup.sh

Changed typo in line 26 apt-add-repository to add-apt-repository.

setup.sh

@@ -23,7 +23,7 @@ sudo apt-get install -y rlwrap
 
 # Install emacs24
 # https://launchpad.net/~cassou/+archive/emacs
-sudo apt-add-repository -y ppa:cassou/emacs
+sudo add-apt-repository -y ppa:cassou/emacs
 sudo apt-get -qq update
 sudo apt-get install -y emacs24-nox emacs24-el emacs24-common-non-dfsg