doc: fix case error of eol attribute in example

The eol attribute only accepts "crlf" and "lf",
but the example incorrectly capitalizes "crlf".

References:

- https://git-scm.com/docs/gitattributes#_eol
- https://github.com/git/git/blob/v2.45.2/convert.c#L1278

Signed-off-by: Shane Sun <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: WaterLemons2k

Documentation/gitattributes.txt

@@ -374,7 +374,7 @@ explicitly define the line endings with `eol` if the `working-tree-encoding`
 attribute is used to avoid ambiguity.
 
 ------------------------
-*.ps1		text working-tree-encoding=UTF-16LE eol=CRLF
+*.ps1		text working-tree-encoding=UTF-16LE eol=crlf
 ------------------------
 
 You can get a list of all available encodings on your platform with the