Ignore mac .DS_Store files

Bug: angleproject:5417
Change-Id: Idc058fe7b66f89bdbf8bcccc453ec15a3c5066e6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2579749
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>

.gitignore

@@ -1,3 +1,4 @@
+.DS_Store
 .vs
 .vscode
 *.Makefile