Update def merge_groups(self): in svg.py

[JasonLLLLLLLLLLL]

From the line 250 to 255, there is a func called merge_groups().
the code is as follows:

    def merge_groups(self):
        path_group = self.svg_path_groups[0]
        for path_group in self.svg_path_groups[1:]:
            path_group.svg_paths.extend(path_group.svg_paths)
        self.svg_path_groups = [path_group]
        return self

The variable path_group is being reused in the for loop, which causes confusion to me when I use this function. Inside the loop, path_group.svg_paths.extend(path_group.svg_paths) doesn't make sense because it is trying to extend path_group.svg_paths with itself. This is likely an error.
I think it is should be(the **group** is the difference between the two codes):

    def merge_groups(self):
        path_group = self.svg_path_groups[0]
        for **group** in self.svg_path_groups[1:]:
            path_group.svg_paths.extend(**group**.svg_paths)
        self.svg_path_groups = [path_group]
        return self

I use a different variable name (group) in the for loop. Here, path_group.svg_paths.extend(group.svg_paths) correctly extends the svg_paths of the first group.
Hopefully, You can notice this message.