MarkupText documentation: ul-tag should be changed to u-tag

[dandavison]

Description of bug / unexpected behavior

This fails with ValueError: Unknown tag 'ul' on line 1 char 13

class MarkupExample(Scene):
    def construct(self):
        text = MarkupText("<ul>underlined</ul>")
        self.add(text)

Expected behavior

The docstring in the code indicates that it should produce underlined text:

manim/manim/mobject/text/text_mobject.py

Line 897 in 9a84ec6

- ``<ul>underline</ul>`` and ``<s>strike through</s>``

Note that this does work:

class MarkupExample(Scene):
    def construct(self):
        text = MarkupText('<span underline="single">underlined</span>')
        self.add(text)

System specifications

Manim Community v0.18.0

[uwezi]

According to the Pango documentation (Pango is the external python library used here), it should be <u>...</u> which actually works

class MarkupExample(Scene):
    def construct(self):
        text = MarkupText("<u>underlined</u>")
        self.add(text)

https://docs.gtk.org/Pango/pango_markup.html

[uwezi]

I have currently not set up a development branch again on my system - perhaps someone could quickly change the docstring? Line 889 in text_mobject.py - or rather line 897 in the current version on Github...