fix flake8 errors

Author: behackl

manim/mobject/mobject.py

@@ -1763,7 +1763,9 @@ def set_color(
         return self
 
     def set_color_by_gradient(self, *colors: Iterable[ParsableManimColor]):
-        """
+        """Set the color of this mobject's submobjects along the specified
+        gradient.
+
         Parameters
         ----------
         colors

manim/utils/color/AS2700.py

@@ -17,7 +17,7 @@
 List of Color Constants
 -----------------------
 
-These hex values (taken from `https://www.w3schools.com/colors/colors_australia.asp`__)
+These hex values (taken from https://www.w3schools.com/colors/colors_australia.asp)
 are non official approximate values intended to simulate AS 2700 colors:
 
 .. automanimcolormodule:: manim.utils.color.AS2700

manim/utils/color/BS381.py

@@ -2,7 +2,7 @@
 
 This module contains colors defined in one of the British Standards
 for colors, BS381C. This standard specifies colors used in identification,
-coding, and other special purposes. See `https://www.britishstandardcolour.com/`__
+coding, and other special purposes. See https://www.britishstandardcolour.com/
 for more information.
 
 To use the colors from this list, access them directly from the module (which
@@ -17,7 +17,7 @@
 List of Color Constants
 -----------------------
 
-These hex values (taken from `https://www.w3schools.com/colors/colors_british.asp`__)
+These hex values (taken from https://www.w3schools.com/colors/colors_british.asp)
 are non official approximate values intended to simulate the ones defined
 in the standard:
 

manim/utils/color/X11.py

@@ -3,7 +3,7 @@
 """X11 Colors
 
 These color and their names (taken from
-`https://www.w3schools.com/colors/colors_x11.asp`__) were developed at the
+https://www.w3schools.com/colors/colors_x11.asp) were developed at the
 Massachusetts Intitute of Technology (MIT) during
 the development of color based computer display system.
 

manim/utils/color/XKCD.py

@@ -18,7 +18,7 @@
 -----------------------
 
 These hex values are non official approximate values intended to simulate the colors in HTML,
-taken from `https://www.w3schools.com/colors/colors_xkcd.asp`__.
+taken from https://www.w3schools.com/colors/colors_xkcd.asp.
 
 .. automanimcolormodule:: manim.utils.color.XKCD