.gitattributes: use the "perl" differ for Perl

As noted in gitattributes(5) this gives better patch context for these
types of files.

Signed-off-by: Ævar Arnfjörð Bjarmason <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: avar

.gitattributes

@@ -1,9 +1,9 @@
 * whitespace=!indent,trail,space
 *.[ch] whitespace=indent,trail,space diff=cpp
 *.sh whitespace=indent,trail,space eol=lf
-*.perl eol=lf
-*.pl eof=lf
-*.pm eol=lf
+*.perl eol=lf diff=perl
+*.pl eof=lf diff=perl
+*.pm eol=lf diff=perl
 /Documentation/git-*.txt eol=lf
 /command-list.txt eol=lf
 /GIT-VERSION-GEN eol=lf