Use a character class to ignore Icon\r directories

This prevents the rule from ending in whitespace, which will get
stripped by tools like Ripgrep, causing any directory named "Icon" to be
invisible.

Global/macOS.gitignore

@@ -2,9 +2,7 @@
 .DS_Store
 .AppleDouble
 .LSOverride
-
-# Icon must end with two \r
-Icon
+Icon[
]
 
 # Thumbnails
 ._*