check connectivity to github.com before installing and/or updating tpm and plugins (2)

.tmux.conf

@@ -1342,7 +1342,7 @@ run 'cut -c3- ~/.tmux.conf | sh -s _apply_configuration'
 #       tmux display 'Done uninstalling tpm and plugins...'
 #     fi
 #   else
-#     if curl -Ikfs -o /dev/null --connect-timeout 2 --max-time 2 https://github.com; then
+#     if git ls-remote -hq https://github.com/gpakosz/.tmux.git master > /dev/null; then
 #       if [ ! -d "$TMUX_PLUGIN_MANAGER_PATH/tpm" ]; then
 #         install_tpm=true
 #         tmux display 'Installing tpm and plugins...'