Update link to Truecolor in the readme (#573)

readme.md

@@ -281,7 +281,7 @@ console.log(foregroundColorNames.includes('pink'));
 
 ## 256 and Truecolor color support
 
-Chalk supports 256 colors and [Truecolor](https://gist.github.com/XVilka/8346728) (16 million colors) on supported terminal apps.
+Chalk supports 256 colors and [Truecolor](https://github.com/termstandard/colors) (16 million colors) on supported terminal apps.
 
 Colors are downsampled from 16 million RGB values to an ANSI color format that is supported by the terminal emulator (or by specifying `{level: n}` as a Chalk option). For example, Chalk configured to run at level 1 (basic color support) will downsample an RGB value of #FF0000 (red) to 31 (ANSI escape for red).