Only change shell if it is not already zsh

setup.sh

@@ -79,7 +79,9 @@ function setup_zsh() {
     zsh -c 'setopt EXTENDED_GLOB; for rcfile in "${ZDOTDIR:-$HOME}"/.zprezto/runcoms/^README.md(.N); do ln -s "$rcfile" "${ZDOTDIR:-$HOME}/.${rcfile:t}"; done'
     cd $HOME
     patch -p0 < $DIR/zsh/prezto.diff
-    chsh -s /bin/zsh
+    if [[ `getent passwd $USER | awk -F: '{print $NF}'` != "/bin/zsh" ]]; then
+        chsh -s /bin/zsh
+    fi
 }
 
 function setup_topydo() {