chore: add version.txt to .gitattributes for style (#966)

* chore: add version.txt to .gitattributes for style

The Knative style check uses linguist to determine if a given file is a
generated file. If so, it excludes that file from the check. This change
should prevent Knative's style check from complaining about no newline on
version.txt

Signed-off-by: Lance Ball <lball@redhat.com>

* fixup: also add zz_filessytem_generated.go

Signed-off-by: Lance Ball <lball@redhat.com>

.gitattributes

@@ -1,3 +1,4 @@
 testdata/repository-a.git/objects/*/* ignore-lint=true
 testdata/repository.git/objects/*/* ignore-lint=true
-
+version.txt linguist-generated=true
+zz_filesystem_generated.go linguist-generated=true