Update canvas.lua docs: hs.drawing -> hs.canvas (#3627)

`hs.drawing` seems to be the old deprecated extension replaced by `hs.canvas`

Author: arthurkarganyan

extensions/canvas/canvas.lua

@@ -2,7 +2,7 @@
 ---
 --- A different approach to drawing in Hammerspoon
 ---
---- `hs.drawing` approaches graphical images as independent primitives, each "shape" being a separate drawing object based on the core primitives: ellipse, rectangle, point, line, text, etc.  This model works well with graphical elements that are expected to be managed individually and don't have complex clipping interactions, but does not scale well when more complex combinations or groups of drawing elements need to be moved or manipulated as a group, and only allows for simple inclusionary clipping regions.
+--- `hs.canvas` approaches graphical images as independent primitives, each "shape" being a separate drawing object based on the core primitives: ellipse, rectangle, point, line, text, etc.  This model works well with graphical elements that are expected to be managed individually and don't have complex clipping interactions, but does not scale well when more complex combinations or groups of drawing elements need to be moved or manipulated as a group, and only allows for simple inclusionary clipping regions.
 ---
 --- This module works by designating a canvas and then assigning a series of graphical primitives to the canvas.  Included in this assignment list are rules about how the individual elements interact with each other within the canvas (compositing and clipping rules), and direct modification of the canvas itself (move, resize, etc.) causes all of the assigned elements to be adjusted as a group.
 ---