gitattributes: make .txt files lf

Otherwise "src\tint\cmd\fuzz\wgsl\dictionary.txt" is checked out as CRLF
on Windows, but we need generated files to be LF, otherwise presubmit
checks fail.

Change-Id: I60fbf40b6731e3f96139117a4738bbf7400bc819
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/210635
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: James Price <jrprice@google.com>
diff --git a/.gitattributes b/.gitattributes
index d149446..037a32c 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -18,4 +18,5 @@
 *.tmpl      eol=lf
 *.tmpl.inc  eol=lf
 *.inl       eol=lf
-*.bat       eol=crlf
+*.txt       eol=lf
+*.bat       eol=crlf
\ No newline at end of file