Fixed #2203 PR.

Reasons for making this change:

Make Icon\r pattern less vulnerable to editors and to auto CRLF → LF conversion on commit. As @spencermathews wrote in #2337 :

Since this ignore rule may be vulnerable to editors that automatically standardize line endings, it seems imperative that updates to this file be done with care or else this rollercoaster seems likely to continue.

Note: the Start..End comment has been added because most editors display Icon[␍] pattern in two lines:

# Start of Icon[\r] pattern
Icon[
]
# End of Icon[\r] pattern

Links to documentation supporting these rule changes:

• How to ignore Icon? in git (Icon[\r])