improve grub.bak existance check

install.sh

@@ -136,9 +136,17 @@ install() {
     prompt -i "\n Setting ${theme} as default..."
 
     # Backup grub config
-    if [[ ! -f "/etc/default/grub.bak" ]]; then
-      cp -an /etc/default/grub /etc/default/grub.bak
-    fi
+	if [[ -f /etc/default/grub.bak ]]; then
+		echo -ne "\n${b_CWAR}File '/etc/default/grub.bak' already exists. Remove it? [yN]${CDEF}"
+		read choice
+		if [ "$choice" = 'y' ]; then
+    		cp -a /etc/default/grub /etc/default/grub.bak
+		else
+			echo -ne "\n${b_CWAR}Skipping to save a backup configuration in '/etc/default/grub.bak'${CDEF}"
+		fi
+	else
+		cp -a /etc/default/grub /etc/default/grub.bak
+	fi
 
     # Fedora workaround to fix the missing unicode.pf2 file (tested on fedora 34): https://bugzilla.redhat.com/show_bug.cgi?id=1739762
     # This occurs when we add a theme on grub2 with Fedora.