Check tmux presence before installing files

install.sh

@@ -19,9 +19,11 @@ ln -sf $DIR/gitconfig ~/.gitconfig
 ln -sf $DIR/bashrc ~/.bashrc
 
 # tmux
-ln -sf $DIR/tmux.conf ~/.tmux.conf
-if [ $INSTALL_ALL -eq 1 ]; then
-    ln -sf $DIR/tmux.clear-keys.conf ~/.tmux.clear-keys.conf
+if which tmux >/dev/null; then
+    ln -sf $DIR/tmux.conf ~/.tmux.conf
+    if [ $INSTALL_ALL -eq 1 ]; then
+        ln -sf $DIR/tmux.clear-keys.conf ~/.tmux.clear-keys.conf
+    fi
 fi
 
 # vim